Tetsuo is a biker in his late twenties or thirties and the adult figurehead of Mitsui's delinquent gang, though he tends to let Mitsui call the shots when they decide to attack the Shohoku basketball team. He's the group's best fighter and most experienced member, and he proves it by taking down five Shohoku players—including Rukawa and Miyagi—before getting brutally beaten by Sakuragi.
Things shift after Mitsui leaves the gang to rejoin the basketball team. When Tetsuo bumps into him on the street after Mitsui's had his knee looked at, he actually respects the decision. He sees Mitsui as an athlete now, not just a gang member.
In the anime, Tetsuo gets challenged for leadership by other members of his gang the morning of Shohoku's match against Shoyo. They corner and beat him up, but Mitsui steps in—except he won't fight back because of a promise to Coach Anzai. Tetsuo takes the hits meant for him, then gets knocked out cold. Sakuragi and his gang show up just in time to break things up, and the incident leads to an unlikely alliance: Tetsuo teams up with Sakuragi's crew to finally take down Ryu and his associates.
Content compiled by AnimeList.moe from publicly available sources.
