One things you guys are forgetting is throat karma can be used to buy stuff. Perhaps getting a time reversal wrist watch is not far fetched. I think Hasumu died years ago and then saved karma to get a time loop watch and then reset just her school to X years ago. It would explain how Chiyo knows...
A twin sister?
I remember it was mentioned that it takes long for a Cupid to be born and they are reborn on their birthday. This 'Ena' had the accident in the field trip but when Chiyo met Ena, she said: it’s been a while. Which implies this Ena has been dead for a long time.
Oof. So being a Cupid forced her to do the very thing she has had enough of.
I also feel sad for Aki. She would be so scared to even confess, talk less love someone after that.