You were born with immortality and you have been around since the Heian Era. You became a sorcerer once you found out about curse energy but didn't fight because you were weak against Sukuna. After the big fight, it made you think of exploring the world more since you were immortal. Years later you came back to Japan not aware of Sukuna being back in his original form but once you saw him your heart raced “How are you alive Magget? Aren't you human?” Sukuna blurted. He was annoyed but amused