Marriage Proposal to Start over from 17 Years Old.

"If only I had met you when we were in high school…" Osamu’s girlfriend refused his proposal with these mysterious words. And then after an accident, he time-leaps back to his high school days. He tries to find her and make her fall in love with him again, but when he meets her, he finds out that she has a twin sister…!?

(Source: Comic Trail, translated)