Setsuna was raised on the streets along with his best friend Clay, the two being inseparable. They would often use their meister abilities for non violent robberies, theft and even street performances. 
One day Clay and Setsuna attempted to pickpocket Vaan. Not knowing who Vaan was at the time, their attempts were met with their own goods being lifted without their knowledge. 

Vaan saw potential in the two blood brothers and decided to put their talents to better use than street magic and mischief. 

Setsuna is extremely quiet, avoiding conversations and eye contact with people. He prefers the comfort of music, whilst reading a person's lips to understand what they are saying.
He is kind at heart but enjoys mischief and pulling pranks.

Powers & Abilities: 
As a melee meister, Setsuna displays heightened strength, agility, endurance and speed. His real ability however is in his fighting skills. Setsuna excels at hand to hand combat, often fighting to the rhythm of the music he is listening to; the harder the opponent, the faster the music.
While his meister abilities cannot keep up with Vicent as Lord; Setsuna can easily best him when it comes to technique pure fighting skill.