6 from High&Low the Worst (2020)

Sinopsis

Fujio Hanaoka, Seiji Kirihara, Shinya Oochi, Masaya Oochi, Madoka Ishii, and Arata Maekawa are close friends who grew up together. While celebrating Seiji's birthday, the group unearths their ten-year-old time capsule, and create a new one, containing penned letters to their future selves, for ten years on. Unbeknownst to the group, they would experience a life-altering tragedy that would not only alter their reality but force them to reassess the verity of their time capsule messages. (Source: AsianWiki)