Joujin Kamen

Otaka Kakuto, a high school boy with a congenital heart condition, moves to Hokkaido to recuperate with his twin sister Katsumi. Kokuto has become friendly with his classmates, but one incident with a monster in the woods triggers a major change in his mind and body. In order to protect his beloved sister (Kokuto), he transcends all restrictions. Here comes the devil in human skin, the masked man!