Percy is a stoic, rather wary man. He genuinely cares about the people in his life, but poor decisions from his past frequently come back to haunt him and get in the way of his relationships with other people. He's quick to defend others and is in general and honorable person; his weapon of choice is a sword which often garners him more attention than he really wants. 

Percy grew up with his brother and half brother in Tokyo. The whole family moved to the USA a long time before the apocalypse, and in that time Percy grew troubled and distant from his family and ended up involved with the mafia. During his work, he became very close with Isaac but the two were separated in a scuffle. Percy was then on his own, eventually ending up in a secret Happy Corporation laboratory designated for genetic testing.