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)  

Ai and Yu, after reading their parent's research and after their parents' disappearance, they decided to go on search for them. They ride a strange train to the Inner World in search of their parents and meets up with Lisa in the train and together they begin their journey within the Inner World.
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(Source: Anime News Network)


Yuka Imai  is a Japanese former voice actress who was previously represented by Gekidan Moonlight and by Atomic Monkey at the time of her retirement. On August 30, 2018, she announced her retirement from voice acting, due to various difficulties in her life such as her divorce and her son having pervasive developmental disabilities. 

(Source: Wikipedia)

Yu Hayakawa