Well demons and humans have the same origin after all, to me it feels like the series was always heading this direction. That's kind of the point of Imuri's character as a demon who teaches the priest about humanity.
Every time Yuri-chan's face half-turns into a beast (sexual), I can't help but remember those twitter profile icons that are an uma musume on the left side and like, a basketball player on the right
Shagrazzat existed before Theo's story. After all, it was one of his favorite books. The series Magus of the Library in-universe is based on Theo's story.
I won't get into the best girl discourse here, but I really do think Yuri-chan is the most IMPORTANT girl for the narrative to exist. It's just like Sou said, she's a special person for Sou and Suzuki (in a manner of speaking)
To be honest, Mirei hasn't realized her feelings at all yet, and if Yushin were to confess now, there's a good chance she would be shocked or even afraid. It's probably too early for these dorks.