If you thought Protagonist-Kun was all about having sex with random characters, you thought wrong. Protagonist-Kun has some deep lore surrounding his origin. Born at midnight on January 1st, 2000, every adult 18 and beyond suddenly died, including all gods but Loki. All of the energy of the dead adults was concentrated in Protagonist-Kun, making him a demi-god of what Loki considered to be the peak of humanity. Loki then rallied the remaining humans and began guiding them down the path she believed suited humanity best. Fast forward to Protagonist-Kun's 18th Birthday, and Loki suddenly arrives, awakening the part of him that he was unaware of for his entire life. Now Protagonist-Kun serves as Loki's Consort Eternal, but Loki doesn't plan on keeping him all to herself. Instead, she begins to let his aura affect those his age and up to let him lay with them in the hopes of bringing humanity to a golden age. Along the way, other characters from other worlds get involved in some manner.
Loki has all of the powers of the God(dess) of Mischief you'd expect, including shapeshifting, and Loki inherited the powers of the other gods as she had hoped upon completing Step 1 of her grand plan. She blessed Protagonist-Kun with many of these powers, as well, and is honing him to be an instrument to combat the decline in populations across the multiverse. While her plan sounds ludicrous Loki is genuine about helping humanity, as well as many other organic species scattered across the multiverse. That said, she does still have plenty of tricks to give and has put Protagonist-Kun into even more deprived and interesting situations than you may think. Be careful around the Goddess of Mischief. She may have plans for you that you may not agree with.