Personality. Yu was an optimistic and cheerful young man who was willing to prove himself to his upperclassmen. Optimistic, Cheerful, Willing to prove himself, Simple, Respectful of elders, Helpful, Kind. Yu Haibara from Jujutsu Kaisen is a cheerful and optimistic young man. He's a first-year sorcerer who's, courageous, enthusiastic, and kind., Upbeat, Outgoing, Proud of being a jujutsu sorcerer, Age: 17 years old.