She's also dumb! When Tsubomi starts her first menstrual cycle she doesn't tell her mother in fear of worrying her. I can forgive that she doesn't know she's having her period but vaginal discharge is not the type of thing one should keep silent about!
It's like an anime version of Are You There God? It's Me, Margaret only worse. There's also a supernatural element to this OVA that, I think, has no business being there. Watch as she learns for the first time what a penis is:
So boys don't also have a vagina?
I don't even know what to say after that.