Yu is a very fierce and determined young girl. She is very confident in her abilities as a martial artist and thus, her ability to make her dreams come true by her own hands. Naturally, she is a very competitive fighter, as she wishes to be the best martial artist in the world, and tries her best not to underestimate her opponents, given her own slim stature. In fact, Yu seems to find pure enjoyment in fighting.
Yu can also be pretty prideful, as she was quick in hearing out Aisha's offer to be on a reality talent show, which she was handpicked to be on, and seems to enjoy being given compliments. However, Yu is also very hotheaded and stubborn. Her drive towards being the best martial artist may cloud her judgement sometimes as she immediately took Aisha's warning as a threat and did whatever she could to stay away from her (granted, Aisha did not help clear up her side of the situation).
World of Winx
Yu makes her debut in the episode "The Shaman," where she is competing in an international martial arts tournament and had made it to the semifinals just before the Winx and Lorelei's arrival. After seeing her through their Dreamix Vision, the Winx (mainly Aisha) try their best to keep a close eye out for their newest enemy, however, the fairies cannot help but be mesmerized by Yu's fighting style as she makes quick work of her opponent and moves onto the finals.
Yu and the Shaman have a fierce final match, but just as it seems as though Yu will come out victorious, she is whisked away by a puff of dark red smoke. She is not seen until later into the episode, where the Winx try to stop the Shaman from pushing a sleepy Yu into a portal into the World of Dreams, but to no avail.
Yu is not seen again until the last episode of the first season, "The Fall of the Queen," where Bloom finds out that the Queen of the World of Dreams, Tinkerbell, had stolen the talent of all of the youths she had brought into the World of Dreams; one of which being Yu's Kung Fu skills. Fortunately, Yu regains her skills once the Winx defeat Tinkerbell and she is seen safe in the WOW Studio during their surprise appearance, ready for the WOW Finals.
Yu is one of the two talents to be targeted by the Shaman, with the other being Madelyn.
She is also one of two talents that had her talent/skill stolen and used during the fight against Tinkerbell, with the other being Annabelle and her voice.
She also shares this trait with Bloom (though she is not a talent), as Tinkerbell had stolen her Dragon's Flame during their fight.
Yu also shares a similar talent in martial arts with another kidnapped talent who remained nameless throughout World of Winx's first season.