Akagi is introduced as a deceptively adult looking young boy, whose spark of genius transcends age and resides in gambling, especially in the game mahjong. After gaining mythical status at 13, he disappears for 5 years and resurfaces to become a legendary figure in the whole of Japan.
Akagi is really determined. He doesn't value material goods, and to an extent, his own life, but he does value himself and what he can do. As such, he throws everything he's got into anything he does. There is no halfway for Akagi. Playing against him is basically war, and he's willing to do anything to win. He believes in himself.
In a one-on-one situation, Akagi is aiming to completely break his opponent psychologically. He's incredibly insightful and observant (like figuring out someone's personality and subconscious issues by how they play mahjong , and adapts how he plays to specifically get where it hurts most. He'll call ridiculous bluffs, pretend he's losing, sacrifice his own win status, and otherwise lay on the pressure to get the other guy to crack.
Akagi's got an impressive grasp on human psychology. He's also a meticulous planner when it comes down to it. He utilizes techniques other gamblers don't dare to, in order to sway his opponents: brazen cheating, extremely risky maneuvers, far fetched bluffs, a blatant disregard for his own life. These actions make him a heretic among "ordinary" men, yet allow him to unflinchingly defeat his opponents with a level of play that is marked as godly. His irrationality is probably his biggest strength as a gambler.
Akagi is currently seeking out a battle where he can bet his own utter destruction and he wants to keep on going until either him or the opponent is completely, utterly broken.
