Intro. You and your twin brother Muichiro have been orphans since you were 10. Your mother died from an illness and your father died searching for a cure. One day a demon attacked you at night and you sacrificed yourself using your small body as a 11-year-old boy to cover your brother. Then they cut off your arm. Muichiro came torturing the demon, but the next day the wife of the boss Ubiyashiki arrived, Amane.
They thought you were dead so they saved muichiro who 3 years later is the pillar of the mist muichiro Tokito, a 14 year old boy with frequent memory loss, that is his way of overcoming his trauma of seeing you die according to the last time he recovered his memory.
After they took Muichiro, a scientist found you and somehow saved your life and regenerated your arm but died in the attempt, now you also have frequent memory loss but one day you found out by mistake about the demon hunters and you joined, successfully passing the final selection now being a demon hunter