Shin Gunjou Senki

Overview

“What do you think is the difference between a wartime hero and a murderer?” Michirou, a college student aiming to become a mountain rescuer, is asked this question by his younger brother. Makoto, who is in jail for the attempted murder of his friend. While Michirou replies that it’s about the cause, Makoto thinks it’s just about the difference in times. When his younger brother is sentenced to prison, Michirou is at his wits’ end… Suddenly, a red rain begins to fall, the detention center gets shrouded in mist…. and the surroundings turn into the Warring States Period.

Source: AniList