Tensei Okita Souji: Shinsengumi Ibun-roku

A new legend of the Shinsengumi is etched into another world!! May 30, 1868. Okita Souji, former captain of the Shinsengumi's First Unit, dies of illness. The swordsman, hailed as the strongest of the late Edo period, ended his short life not on the battlefield, but in his bed. —And that's how this man was reincarnated into another world where people fight with magic!? Okita was reincarnated as a boy named Rikuru, who was physically weak and neglected by his family because he didn't possess any magical abilities. Despite his unhappy circumstances, he found happiness in being able to move his body. Aiming to train his body and become stronger, Okita overwhelms those who mock him with his natural swordsmanship. Amidst all this, Okita realizes that there's a possibility that other members of the Shinsengumi have also been reincarnated. "This time, I want to fight alongside everyone in the Shinsengumi until the very end," Okita thinks, when a certain person appears before him...? The genius swordsman, Okita Souji, slashes through otherworldly magic!! (Source: Jitsugyo no Nihon Sha, translated)