Samurai Swordfish.

Edo, 1863. Aisuke Kajiki, a young blind swordsman, is entrusted the son of his best friend Toramaru Sakakibara, who is about to join the Shogun's Samurai Unit and promises to train him well. However, after Toramaru's death in battle, Eisuke drowns in a river and is transported in time to present-day Tokyo. Eisuke and his descendant, Ryusei, a college student, go to meet Toramaru's descendant, Taiga, a swimmer. The blind samurai's promise to his best friend in Edo is fulfilled 160 years later in present-day Tokyo through para-swimming.