Tachibana Tatsumi (立花辰巳 Tachibana Tatsumi, たちばな たつみ Tachibana Tatsumi) is a 3rd Year student of Nekketsu High School. He is first introduced in Downtown Nekketsu Baseball Monogatari: Yakyū de Shōbu da! Kunio-kun. An honor student, he was previously the captain of the school's baseball club, but he was unable to play in the Summer Koshien due to a shoulder injury. Because of this, he stopped playing baseball, to the shock of his ill girlfriend Rika. When Sugata attempts to revive the baseball club, Tachibana joins once again with renewed spirit.
- Though he has a similar face, Sadao from Ike Ike! Nekketsu Hockey Bu: Subette Koronde Dairantō, who is the captain of the school's baseball club in that game, is not the same character as Tachibana.