Owari ni Hajimeru Koi no Hanashi

The earth is going be destroyed in one year due to a comet collision. Childhood friends Luka and Chihiro, who live under one roof in a seaside town, go about their daily lives as usual, not realizing that they may die in one year. When Luka is given an assignment by his school to think about what he wants to do before he dies in order to make the most of the rest of his life, he decides that he wants to "fall in love" with Chihiro, who has always been special to him.... When he learns of the "end," he realizes how strongly he falls in love with him.

(Arca comics, translated)