The premise is a girl has a crush on a younger boy who is smart, but neither are able to admit their feelings. One day, a mysterious guy appears before her who looks just like an older version of her crush. Turns out it is the same boy from the future who came back in time to "steal her away", when in fact he is making sure they get together as they get married in the future. In the end, the guy actually came back to see his wife in highschool because in the future she is too busy for him. Thanks in advance!

Ooh I love this oneshot. It's in a collection called Ghost wa Kiss o Kirau story 2.

I'm in idol hell T.T

Thank you so much!