Surprised this isn't translated yet. AFAIK this was originally the 1st of a 3 chapter story, the 2nd being "Watashi wa, Kanojo o aishite iru". 3rd chapter showed the protag from ch1, possessing the girls from ch2. These were sold as doujins at Comic Market with samples on Pixiv, but the author removed all from the internet. Only this chapter got redrawn and sold digitally.
Summary: Protag has extremely detailed possession sexual fantasies of young girls he sees. But it's a pervert's single pride that he would never lay a hand on any of them. One day, a schoolgirl claiming to be the god of fantasies/delusions appears to him in a dream, and gives him the ability to actualize his fantasies in reality. He wakes up, sees a girl being interviewed on a live broadcast. Starts fantasizing about possessing her, and suddenly becomes her.
He panicks, hides in a stall and realizes how small the girl is. He tries to will himself back to his own body, but doesn't know how. Unsure of whether his inability to hold pee is because of being the young girl or part of his fantasy, he feels guilt for fantasizing and possessing the girl. What if he can't go back and ends up being stuck as her? He then convinces himself that enacting his entire sexual fantasy out is for her sake, so she can get her body back. Two lolicons enter the public toilet. Protag tries to keep quiet but questions whether this is all part of his fantasy, and if it's actually reality. He can't control himself, and forgot to lock the stall door.
After he goes back to himself, he runs to the same place to confirm that it was reality or not, and finds the girl. Everything was exactly according to his fantasy. He blames himself, but knows it's impossible for him to stop fantasizing. He calls the cops to rescue the girl, looks up and sees another girl. Before he realizes it, he fantasizes about and possesses her. Now that he's lost his pride of not harming anyone, nothing is holding him back anymore.