Yu is Ai's younger twin brother. Always sure to introduce himself when he meets someone new, he shows no signs of shyness, even towards someone like Kaze (who is surrounded by such an unapproachable aura). Yu tends to act like an adult in that he always proceeds with caution along their journey. But he also has an innocent, childish side that can be seen in such acts as mindlessly chasing cute animals like Chocobo. Through the use of Penna, he can converse with Chobi. (Source: Wikipedia)