Douka Ore o Houtte Oitekure: Nazeka Bocchi no Owatta Koukou Seikatsu o Kanojo ga Kaeyou to shitekuru

Love, friendship, and a glorious adolescence—that's what Hodoka Nanamura hoped for when he entered high school. But by his final year, he had none of it. Then, on the eve of graduation, he sacrifices himself to save his classmate, Sora Hanamitsuji, from on oncoming truck, ending his life... or so it should have. Instead, he and Hanamitsuji were both transported back in time to their first year of high school, just before the entrance ceremony. Though Nanamura resigned himself to reliving the same unremarkable, lonely high school years, Hanamitsuji swears that she'll drag him out of his loner lifestyle!

*Source: Manga UP! Global*