Second Summer, Never See You Again summary:

Moriyama Rin was born with an incurable disease. Despite her best efforts to live a normal high school life, Shimehara Satoshi was the one who ruined it at the very end.'I wish I didn't say I liked her.'Satoshi, full of regrets, experiences a time leap and meets Rin for the second time.'If I don't involve myself with her, Rin will be able to spend her short time left and end it with a smile...'