I'd certainly love to visit this shrine.
Great ending though. "Give me some time"? Bloody heck man, the correct thing to do was to accept right then and there and make her your wife!
Gramps doesn't know that the boy is not a reincarnation, but just the normal hentai protagonist. All hentai protagonists emanate a hige power and aura from their groin...
As she said at the beginning, nobody really comes to the shrine other than to ridicule it. Also her purpose in the ritual was to summon Karidaka to the world. She could have meant any old penis but then she also talks about yorishiro, which implies the spirit of Karidaka himself. Since Shinta is the incarnation of Karidaka she would have fulfilled the purpose of the ritual.
As long as there is informed affirmative consent (and everybody stands up to the jackasses who show up at the Shrine to gawk), I don't see a problem with either situation.
PS to clarify, minors cannot give INFORMED consent to sex with adults. When it happens in hentai, and "Sailor Moon", that's called fantasy. Â