Tidus.

Essence and form conflicted- Hes not really alive. Hes ppart of the zanarkand dream thing, therefore even though his form seems solid, hes really just made of pyreflies.
Brash yet painfully shy- He goes without thinking, like in the trials where he goes to yuna.
Demure yet disobendient- he likes to play around, and doesnt always listen,
The smallest yet powerful- Youngest of the warriors, possibly shortest, but he can be super-good.