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1boy 1girl 2020s 2023 2d 2d_(artwork) animated_skeleton artist_name artist_watermark blue_breasts blue_nipples blue_tongue bottom_sans breasts clothed clothed_male clothing cum cum_on_face digital_media_(artwork) duo ech7474 ectopenis female_sans gaster gaster_(undertale) genderswap genderswap_(mtf) genitals gloves hooded_jacket hoodie jacket licking licking_face licking_penis male male/female monster multiple_views nipples nude off_shoulder orange_penis paizuri penis purple_background rule_63 sans sans_(undertale) sanster seme_gaster sex simple_background skeleton solid_color_background sweater tears top_gaster twitter uke_sans undead undertale undertale_(series) video_game_character video_games watermark white_gloves
1boy 1girl 2020s 2023 2d 2d_(artwork) animated_skeleton artist_name artist_watermark blue_breasts blue_nipples blue_tongue bottom_sans breasts clothed clothed_male clothing cum cum_on_face digital_media_(artwork) duo ech7474 ectopenis female_sans gaster gaster_(undertale) genderswap genderswap_(mtf) genitals gloves hooded_jacket hoodie jacket licking licking_face licking_penis male male/female monster multiple_views nipples nude off_shoulder orange_penis paizuri penis purple_background rule_63 sans sans_(undertale) sanster seme_gaster sex simple_background skeleton solid_color_background sweater tears top_gaster twitter uke_sans undead undertale undertale_(series) video_game_character video_games watermark white_gloves
2010s 2016 2boys 2d 2d_(artwork) animated_skeleton arms_behind_back artist_name beoteono black_tentacles blue_blush blue_penis blush bodily_fluids bottom_sans buttercupsticks clothed clothing cussing dominant dominant_male drooling duo ectopenis feet_out_of_frame fluids gaster gaster_(undertale) grabbing_another's_chin grabbing_chin grey_background hand_under_chin hands_behind_back male male/male male_focus male_only maledom malesub monster one_eye_closed partially_colored penis precum profanity sans sans_(undertale) sanster seme_gaster simple_background skeleton soul soul_sex submissive submissive_male swearing tentacle tentacle_on_male tentacles tentacles_around_legs tentacles_on_male text top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2010s 2016 2boys 2d 2d_(artwork) animated_skeleton arms_behind_back artist_name beoteono black_tentacles blue_blush blue_penis blush bodily_fluids bottom_sans buttercupsticks clothed clothing cussing dominant dominant_male drooling duo ectopenis feet_out_of_frame fluids gaster gaster_(undertale) grabbing_another's_chin grabbing_chin grey_background hand_under_chin hands_behind_back male male/male male_focus male_only maledom malesub monster one_eye_closed partially_colored penis precum profanity sans sans_(undertale) sanster seme_gaster simple_background skeleton soul soul_sex submissive submissive_male swearing tentacle tentacle_on_male tentacles tentacles_around_legs tentacles_on_male text top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2010s 2017 2d 2d_(artwork) 4boys animated_skeleton blue_blush blue_tongue blush bottom_sans bukkake clothed clothing cum cum_in_mouth cum_on_tongue digital_media_(artwork) ectotongue fangs finger_in_mouth fontcest gangbang gaster grillby grillsans hand implied_incest lowest-of-dirt lowest_of_dirt male male/male male_only monster multiple_boys one_eye_closed orange_cum orange_penis papyrus papyrus_(undertale) papysans penis red_background sans sans_(undertale) sanster seme_gaster seme_grillby seme_papyrus sex skeleton solo_focus tongue top_gaster top_grillby top_papyrus tumblr uke_sans undead undertale undertale_(series) unseen_character unseen_male unseen_male_face upper_body video_game_character video_games yaoi
2010s 2017 2d 2d_(artwork) 4boys animated_skeleton blue_blush blue_tongue blush bottom_sans bukkake clothed clothing cum cum_in_mouth cum_on_tongue digital_media_(artwork) ectotongue fangs finger_in_mouth fontcest gangbang gaster grillby grillsans hand implied_incest lowest-of-dirt lowest_of_dirt male male/male male_only monster multiple_boys one_eye_closed orange_cum orange_penis papyrus papyrus_(undertale) papysans penis red_background sans sans_(undertale) sanster seme_gaster seme_grillby seme_papyrus sex skeleton solo_focus tongue top_gaster top_grillby top_papyrus tumblr uke_sans undead undertale undertale_(series) unseen_character unseen_male unseen_male_face upper_body video_game_character video_games yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) ??? anal anal_fisting animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page comic_panel cuntboy digital_media_(artwork) double_penetration drooling ectopussy edit edited english_text fingers_in_pussy fisting fisting_pussy gaster gaster_(undertale) grabbing_mouth large_filesize long_image male male/cuntboy monochrome monster mouth_held_open multiple_hands nczhhdyb pants_pulled_down pants_pulling pussy pussy_juice sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus spoken_heart spoken_question_mark spread_anus spread_pussy tears text third-party_edit tongue tongue_out top_gaster uke_sans uncensored undead undertale undertale_(series) urethra vaginal vaginal_fisting video_games wet_pussy yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) ??? anal anal_fisting animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page comic_panel cuntboy digital_media_(artwork) double_penetration drooling ectopussy edit edited english_text fingers_in_pussy fisting fisting_pussy gaster gaster_(undertale) grabbing_mouth large_filesize long_image male male/cuntboy monochrome monster mouth_held_open multiple_hands nczhhdyb pants_pulled_down pants_pulling pussy pussy_juice sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus spoken_heart spoken_question_mark spread_anus spread_pussy tears text third-party_edit tongue tongue_out top_gaster uke_sans uncensored undead undertale undertale_(series) urethra vaginal vaginal_fisting video_games wet_pussy yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) ??? anal anal_fisting animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page comic_panel cuntboy digital_media_(artwork) double_penetration drooling ectopussy edit edited english_text fingers_in_pussy fisting fisting_pussy gaster gaster_(undertale) grabbing_mouth large_filesize long_image male male/cuntboy monochrome monster mouth_held_open multiple_hands nczhhdyb pants_pulled_down pants_pulling pussy pussy_juice sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus spoken_heart spoken_question_mark spread_anus spread_pussy tall_image tears text third-party_edit tongue tongue_out top_gaster uke_sans uncensored undead undertale undertale_(series) urethra vaginal vaginal_fisting video_games wet_pussy yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) ??? anal anal_fisting animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page comic_panel cuntboy digital_media_(artwork) double_penetration drooling ectopussy edit edited english_text fingers_in_pussy fisting fisting_pussy gaster gaster_(undertale) grabbing_mouth large_filesize long_image male male/cuntboy monochrome monster mouth_held_open multiple_hands nczhhdyb pants_pulled_down pants_pulling pussy pussy_juice sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus spoken_heart spoken_question_mark spread_anus spread_pussy tall_image tears text third-party_edit tongue tongue_out top_gaster uke_sans uncensored undead undertale undertale_(series) urethra vaginal vaginal_fisting video_games wet_pussy yaoi
2boys 2d 2d_(artwork) ahegao animated_skeleton artist_request blue_tongue blush bottom_sans crying_with_eyes_open dominant_pov english_text fangs gaster gaster_(undertale) hands hands_behind_head male male/male male_ahegao male_focus male_only moan monster multiple_hands pleasure_face pov sans sans_(undertale) sanster seme_gaster skeleton solo_focus text tongue tongue_out top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2boys 2d 2d_(artwork) ahegao animated_skeleton artist_request blue_tongue blush bottom_sans crying_with_eyes_open dominant_pov english_text fangs gaster gaster_(undertale) hands hands_behind_head male male/male male_ahegao male_focus male_only moan monster multiple_hands pleasure_face pov sans sans_(undertale) sanster seme_gaster skeleton solo_focus text tongue tongue_out top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) anal anal_fisting animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page comic_panel cuntboy double_penetration drooling ectopussy fisting fisting_pussy gaster gaster_(undertale) grabbing_mouth male male/cuntboy monochrome monster mouth_held_open multiple_hands nczhhdyb pussy sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus tears tongue tongue_out top_gaster uke_sans uncensored undead undertale undertale_(series) vaginal vaginal_fisting video_games yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) anal anal_fisting animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page comic_panel cuntboy double_penetration drooling ectopussy fisting fisting_pussy gaster gaster_(undertale) grabbing_mouth male male/cuntboy monochrome monster mouth_held_open multiple_hands nczhhdyb pussy sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus tears tongue tongue_out top_gaster uke_sans uncensored undead undertale undertale_(series) vaginal vaginal_fisting video_games yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) ??? animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page cuntboy ectopussy fingers_in_pussy gaster gaster_(undertale) male male/cuntboy monochrome monster multiple_hands nczhhdyb pants_pulled_down pants_pulling pussy pussy_juice sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus spoken_heart spoken_question_mark spread_anus spread_pussy top_gaster uke_sans uncensored undead undertale undertale_(series) urethra video_games wet_pussy yaoi
1boy 1cuntboy 2010s 2017 2d 2d_(artwork) ??? animated_skeleton anus black_and_white bottom_sans clitoris comic comic_page cuntboy ectopussy fingers_in_pussy gaster gaster_(undertale) male male/cuntboy monochrome monster multiple_hands nczhhdyb pants_pulled_down pants_pulling pussy pussy_juice sans sans_(undertale) sanster seme_gaster sequence sequential skeleton solo_focus spoken_heart spoken_question_mark spread_anus spread_pussy top_gaster uke_sans uncensored undead undertale undertale_(series) urethra video_games wet_pussy yaoi
1:1 1:1_aspect_ratio 2d 2d_(artwork) animated_skeleton blue_blush blue_tongue bottom_sans daron9 gaster gaster_(undertale) implied_penetration implied_sex korean_text male monster sans sans_(undertale) sanster seme_gaster skeleton solo_focus text tongue tongue_out top_gaster uke_sans undead undertale undertale_(series) unseen_male_face video_games
1:1 1:1_aspect_ratio 2d 2d_(artwork) animated_skeleton blue_blush blue_tongue bottom_sans daron9 gaster gaster_(undertale) implied_penetration implied_sex korean_text male monster sans sans_(undertale) sanster seme_gaster skeleton solo_focus text tongue tongue_out top_gaster uke_sans undead undertale undertale_(series) unseen_male_face video_games
2015 2d 2d_(artwork) animated_skeleton black_background blue_blush blush bottom_sans clothed duo gaster gaster_(undertale) groping hand hand_on_crotch hands male monster multiple_hands sans sans_(undertale) sanster seme_gaster shirt_up skeleton solo_focus suckmytrombone sweater top_gaster uke_sans undead undertale undertale_(series) video_games
2015 2d 2d_(artwork) animated_skeleton black_background blue_blush blush bottom_sans clothed duo gaster gaster_(undertale) groping hand hand_on_crotch hands male monster multiple_hands sans sans_(undertale) sanster seme_gaster shirt_up skeleton solo_focus suckmytrombone sweater top_gaster uke_sans undead undertale undertale_(series) video_games
2020s 2022 2d 2d_(artwork) animated_skeleton arm_grab bad_id bad_twitter_id black_and_white bottom_sans clothed covering_mouth digital_media_(artwork) fingering fingering_another fingering_partner gaster gaster_(undertale) grabbing_arm grabbing_hand hand hand_grab hand_on_mouth hands inactive_account male male_focus male_only monochrome monster monster_boy multiple_hands non-con non-consensual noncon nonconsensual pants_pull pants_pulled_down sans sans_(undertale) sanster seme_gaster shirt_lift shirt_pull shirt_up simple_background skeleton socks_on solo_focus top_gaster toubigaizi twitter uke_sans undead undertale undertale_(series) undressing unseen_character unseen_male_face video_game_character video_games white_hair yaoi
2020s 2022 2d 2d_(artwork) animated_skeleton arm_grab bad_id bad_twitter_id black_and_white bottom_sans clothed covering_mouth digital_media_(artwork) fingering fingering_another fingering_partner gaster gaster_(undertale) grabbing_arm grabbing_hand hand hand_grab hand_on_mouth hands inactive_account male male_focus male_only monochrome monster monster_boy multiple_hands non-con non-consensual noncon nonconsensual pants_pull pants_pulled_down sans sans_(undertale) sanster seme_gaster shirt_lift shirt_pull shirt_up simple_background skeleton socks_on solo_focus top_gaster toubigaizi twitter uke_sans undead undertale undertale_(series) undressing unseen_character unseen_male_face video_game_character video_games white_hair yaoi
2d 2d_(artwork) animated_skeleton bigger_dom bigger_dom_smaller_sub bigger_male bigger_penetrating bigger_penetrating_smaller blue_blush blue_tongue bottom_sans english_text from_behind gaster gaster_(undertale) heart-shaped_pupils heart_eyes humanoid humanoid_penetrating larger_male larger_penetrating larger_penetrating_smaller male male_penetrating monochrome nude one_eye_closed penetration sans sans_(undertale) sanster seme_gaster sex sex_from_behind skeleton small_sub small_sub_big_dom smaller_penetrated smaller_sub smaller_sub_bigger_dom tesno204 text tongue tongue_out top_gaster topless topless_male uke_sans undead undertale undertale_(series) video_games
2d 2d_(artwork) animated_skeleton bigger_dom bigger_dom_smaller_sub bigger_male bigger_penetrating bigger_penetrating_smaller blue_blush blue_tongue bottom_sans english_text from_behind gaster gaster_(undertale) heart-shaped_pupils heart_eyes humanoid humanoid_penetrating larger_male larger_penetrating larger_penetrating_smaller male male_penetrating monochrome nude one_eye_closed penetration sans sans_(undertale) sanster seme_gaster sex sex_from_behind skeleton small_sub small_sub_big_dom smaller_penetrated smaller_sub smaller_sub_bigger_dom tesno204 text tongue tongue_out top_gaster topless topless_male uke_sans undead undertale undertale_(series) video_games
2boys 2d 2d_(artwork) anal animated_skeleton bigger_dom bigger_dom_smaller_sub bottom_sans carrying carrying_partner carrying_position cussing digital_media_(artwork) dominant dominant_male domination duo ectopenis english_text gaster gaster_(undertale) gay in_heat licking_face male male/male male_focus male_only maledom malesub monster monster_boy penis profanity reverse_stand_and_carry_position reverse_suspended_congress sans sans_(undertale) sanster seme_gaster sex simple_background skeleton sketch small_sub small_sub_big_dom smaller_male smaller_sub smaller_sub_bigger_dom spoopy-gaster submissive submissive_male swearing tentacle tentacle_around_penis tentacle_on_male tentacle_sex text text_bubble top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2boys 2d 2d_(artwork) anal animated_skeleton bigger_dom bigger_dom_smaller_sub bottom_sans carrying carrying_partner carrying_position cussing digital_media_(artwork) dominant dominant_male domination duo ectopenis english_text gaster gaster_(undertale) gay in_heat licking_face male male/male male_focus male_only maledom malesub monster monster_boy penis profanity reverse_stand_and_carry_position reverse_suspended_congress sans sans_(undertale) sanster seme_gaster sex simple_background skeleton sketch small_sub small_sub_big_dom smaller_male smaller_sub smaller_sub_bigger_dom spoopy-gaster submissive submissive_male swearing tentacle tentacle_around_penis tentacle_on_male tentacle_sex text text_bubble top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2022 2d 2d_(artwork) animated_skeleton blue_blush blue_hoodie blue_jacket blush bottom_sans bound bound_arms chains clothed digital_media_(artwork) disembodied_hands dominant_pov drooling ectoplasm fingering fingering_another fingering_partner gaster hooded_jacket hoodie jacket japanese_text leg_grab legs_apart logo_(pixiv_id_30462562) looking_at_viewer male monster monster_boy partially_clothed partially_nude potion pov restrained restraints sans sans_(undertale) sanster seme_gaster skeleton solo_focus submissive sweat text top_gaster uke_sans undead undertale undertale_(series) unseen_male unseen_male_face video_games yaoi
2022 2d 2d_(artwork) animated_skeleton blue_blush blue_hoodie blue_jacket blush bottom_sans bound bound_arms chains clothed digital_media_(artwork) disembodied_hands dominant_pov drooling ectoplasm fingering fingering_another fingering_partner gaster hooded_jacket hoodie jacket japanese_text leg_grab legs_apart logo_(pixiv_id_30462562) looking_at_viewer male monster monster_boy partially_clothed partially_nude potion pov restrained restraints sans sans_(undertale) sanster seme_gaster skeleton solo_focus submissive sweat text top_gaster uke_sans undead undertale undertale_(series) unseen_male unseen_male_face video_games yaoi
2020s 2022 2d 2d_(artwork) animated_skeleton blue_blush blue_hoodie blue_jacket blue_tongue blush bottom_sans clothed crying digital_media_(artwork) duo gaster hooded_jacket hoodie jacket japanese_text logo_(pixiv_id_30462562) male male_penetrating monster monster_boy penetration sans sans_(undertale) sanster seme_gaster sex skeleton submissive sweat tears text tongue top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2020s 2022 2d 2d_(artwork) animated_skeleton blue_blush blue_hoodie blue_jacket blue_tongue blush bottom_sans clothed crying digital_media_(artwork) duo gaster hooded_jacket hoodie jacket japanese_text logo_(pixiv_id_30462562) male male_penetrating monster monster_boy penetration sans sans_(undertale) sanster seme_gaster sex skeleton submissive sweat tears text tongue top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2017 2d 2d_(artwork) animated_skeleton blue_blush blue_tongue blush bottom_sans crying crying_with_eyes_open from_behind gaster gaster_(undertale) grabbing_pillow male male_penetrating monster penetration sans sans_(undertale) sanster seme_gaster sex sinfulsanspar skeleton smiling tears tongue tongue_out top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2017 2d 2d_(artwork) animated_skeleton blue_blush blue_tongue blush bottom_sans crying crying_with_eyes_open from_behind gaster gaster_(undertale) grabbing_pillow male male_penetrating monster penetration sans sans_(undertale) sanster seme_gaster sex sinfulsanspar skeleton smiling tears tongue tongue_out top_gaster uke_sans undead undertale undertale_(series) video_games yaoi
2020s 2022 2boys 2d 2d_(artwork) abosinsin animated_skeleton bad_id bad_twitter_id big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bigger_male bigger_penetrating bigger_penetrating_smaller blue_blush blue_penis blush bottom_sans commission_art dialogue digital_media_(artwork) duo ectopenis ectoplasm edging english_text face_grab gaster gaster_(undertale) gay gay_sex grabbing_face grabbing_penis holding_face inactive_account larger_penetrating male male/male male_only male_penetrated male_penetrating male_penetrating_male monster orgasm_denial partially_colored penetration penis penis_grab purple_blush purple_penis sans sans_(undertale) sanster seme_gaster sitting skeleton small_sub small_sub_big_dom smaller_male smaller_penetrated smaller_sub smaller_sub_bigger_dom text third-party_source top_gaster twitter_username uke_sans undead undertale undertale_(series) video_game_character video_games white_background yaoi
2020s 2022 2boys 2d 2d_(artwork) abosinsin animated_skeleton bad_id bad_twitter_id big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bigger_male bigger_penetrating bigger_penetrating_smaller blue_blush blue_penis blush bottom_sans commission_art dialogue digital_media_(artwork) duo ectopenis ectoplasm edging english_text face_grab gaster gaster_(undertale) gay gay_sex grabbing_face grabbing_penis holding_face inactive_account larger_penetrating male male/male male_only male_penetrated male_penetrating male_penetrating_male monster orgasm_denial partially_colored penetration penis penis_grab purple_blush purple_penis sans sans_(undertale) sanster seme_gaster sitting skeleton small_sub small_sub_big_dom smaller_male smaller_penetrated smaller_sub smaller_sub_bigger_dom text third-party_source top_gaster twitter_username uke_sans undead undertale undertale_(series) video_game_character video_games white_background yaoi
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bodily_fluids bottom_sans clothed clothed/nude completely_naked completely_nude crying duo fingering fingering_another fingering_partner fluids fully_clothed gaster gaster_(undertale) humanoid male male/male monochrome monster monster_boy naked nude pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom tears top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games white_background yaoi
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bodily_fluids bottom_sans clothed clothed/nude completely_naked completely_nude crying duo fingering fingering_another fingering_partner fluids fully_clothed gaster gaster_(undertale) humanoid male male/male monochrome monster monster_boy naked nude pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom tears top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games white_background yaoi
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub blush_lines bottom_sans duo gaster gaster_(undertale) humanoid male male/male monochrome monster monster_boy one_eye_closed pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom sweat top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games yaoi
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub blush_lines bottom_sans duo gaster gaster_(undertale) humanoid male male/male monochrome monster monster_boy one_eye_closed pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom sweat top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games yaoi
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bodily_fluids bottom_sans bottomless duo fingering fingering_another fingering_partner fluids gaster gaster_(undertale) humanoid lab_coat labcoat male male/male monochrome monster monster_boy pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bodily_fluids bottom_sans bottomless duo fingering fingering_another fingering_partner fluids gaster gaster_(undertale) humanoid lab_coat labcoat male male/male monochrome monster monster_boy pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bottom_sans clothed/nude duo ectoplasm fingering gaster gaster_(undertale) humanoid male male/male male_only monochrome monster monster_boy pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games yaoi
2010s 2018 2d 2d_(artwork) animated_skeleton big_dom big_dom_small_sub bigger_dom bigger_dom_smaller_sub bottom_sans clothed/nude duo ectoplasm fingering gaster gaster_(undertale) humanoid male male/male male_only monochrome monster monster_boy pf-pro-fucker pf_pro_fucker sans sans_(undertale) sanster seme_gaster skeleton small_sub small_sub_big_dom smaller_sub smaller_sub_bigger_dom top_gaster tumblr uke_sans undead undertale undertale_(series) video_game_character video_games yaoi