"Fire! Fire! Oh, that's just me"
Kasai is a confident young man who sometimes lets his confidence tend towards overconfidence. He's a hot-headed youth who can be angered easily but cools off almost as quickly. His friends tend to find this quirk of his amusing and often rile him up simply to see him get angry and then laugh about it with him a few seconds later. However this sense of confidence combined with his angry nature makes for an extremely determined fighter who usually refuses to give up until he's unable to move or his opponent is. He is very outspoken and will speak his mind to just about anyone, including those who technically he shouldn't talk back to such as teachers.
Kasai never knew his real parents but that never really bothered him. He was raised by an aunt and an uncle who thought the world of him and were more than happy to raise him as their own. He had an enjoyable childhood without any major worries which leaves one to wonder where his temper came from. The cause became apparent when he turned ten, however.
He was walking a girl from his school that he was sweet on home when the two of them were set on by a group of older boys. The group pulled the two apart and beat Kasai repeatedly until he was barely able to focus let alone stand and then they dragged the pair of them out of sight behind a nearby building. Once there they began abusing the girl as well, leaving Kasai slumped on the ground. The girl screamed as various articles of clothing were torn off and the boys' rough hands began to grab at her.
No one noticed the gradual increase of the surrounding temperature, being as busy as they were terrorizing the girl. Suddenly the leader of the boys simply incinerated, his scream of pain cut short as he turned to ashe. The group of boys spun around to see Kasai, now wearing a red haori and fully robed in fire with wings of sheer heat spreading from his back and a halberd larger then the boy himself strapped to his back. But it wasn't his appearance that attracted their attention, it was his eyes. His eyes burned hotter then his body with a hot-white light of pure, uncontrolled rage which shone out from his face like beacons. He released an inhuman yell of rage that sounded more like the shriek of a humongous bird, snapping the boys out of their stupor and causing them to scramble to their feet and attempt to run but Kasai lashed out with tendrils of fire, each one a whip of heat that cracked as they connected with each fleeing boy. With each connection there was a brief scream and then nothing but a pile of ashes floating in the wind as the boys' very essence was burned.
Eventually there were no more boys and Kasai slowly settled back to the ground as the fire about his body subsided and his strange clothing returned to normal. Kasai slumped to his knees and then to his hands as he retched, the horror of what he had done catching up to him. Eventually he ran out of anything to heave up and simply fell over, attempting to catch his breath. The girl slowly gathered her clothing and backed away from Kasai, fear plain in her eyes. Once a far enough distance away the girl turned and sprinted for home, tears trailing from her eyes as she ran. Kasai slowly struggled to his feet and limped his way back home, exhausted beyond measure and still feeling the pains of his earlier beating.
The next day the paper was filled with reports about the missing boys and how everyone was looking for them but no one had any information. As the days went by the fluster died down and things returned to normal for everyone. Everyone except Kasai that is. He had to keep careful reigns on his powers now to prevent them from unleashing themselves once again and that turned everyday into a challenge. As Kasai aged he got better control over his powers and it no longer threatened to escape every time he got mad but he still had the habit of quickly defusing any anger he felt which caused no end of mirth to his friends.