Yori is described as being dimutive in stature, and is described as being "mousey," but he possesses great wisdom and intelligence, being Sensei Yamada's star pupil and finding his tricky riddles relatively easy to solve. Though he may seem timid he is capable of great courage and defends Jack.
Initially, Yori is shy and timid. But he is also capable of great courage and loyalty. In later books he is more aware of his courage and will defend his friends to the last.
Yori is the voice of wisdom on the group, taking after his mentor and friend Sensei Yamada.