Sekai de Ichiban Hayai Haru

Haruta Mahoro is a manga artist whose first series became a huge bestseller. Her publisher expects her sophomore effort to be even better. There's just one problem: Mahoro has no idea what to draw next, because she plagiarized the story that skyrocketed her to stardom from a high school classmate named Yukishima, who shared a few precious months with Mahoro in the school's manga club before passing away and leaving her his notebook filled with all his story ideas. When, after a strange encounter, Mahoro wakes up ten years in the past—around the time of her first meeting with Yukishima—she realizes this could be her chance to redeem herself, erase her regrets, and maybe even save Yukishima's life...

(Source: Kodansha USA)