Tidus

Tidus is a minor character in the Kingdom Hearts series, originally from Final Fantasy X.

Kingdom Hearts: Light by Darkness
Final Fantasy X

''An athletic boy with a sunny personality and tons of energy. He is highly confident in his fighting abilities, and usually asks to spar with Sora. ''

Most of the time you will see him in good spirits, and you rarely see him not in a good mood.

Kingdom Hearts: Light by Darkness
You first see Tidus when Sora is walking to school. Tidus challenges Sora to a sparring match, in which Sora agrees to. After Sora beats him, Tidus sighs, but quickly goes back to his optimistic personality, and walks to school. During the world's Heartless invasion, Tidus is seen fending off the Heartless with his sword.

Afterward, Tidus is an optional boss for all three playable characters, and also gives a quest to the player.