This chapter has a really weird progression for Mai's character. Not a fan of horror manga randomly having a sex scene. I actually don't fully blame Hikaru for once though. Guy's kinda going crazy wondering if he's even human and sex is probably the ultimate form of human contact, his internal monologue demonstrates how it helps him think of himself as human. He's looking for anything to help ground himself. This is one of the few scenarios I'd OK a random sex scene.
Still not a fan of him doing it with Mai. Would have been much natural with Chizuru since he, you know, actually loves her. Mai randomly coming up to him for sex because she wants to bear "god's child" is just, well, random. The whole scene feels clunky and unnatural.