Ano Hi Mita Hana no Namae wo Bokutachi wa Mada Shiranai. Movie

劇場版 あの日見た花の名前を僕達はまだ知らない。

A year after their deceased friend Honma Meiko appeared to them, Jinta Yadomi and the other members of the Super Peace Busters decide to write letters in her memory. Attempting to enjoy their summer together, they reminisce about their time together before and after her death.

AnoHana. Movie retells the main events of the parent story in the perspective of each member of the Super Peace Busters.

(Source: MAL Rewrite)