Tatsumi fought in Shooto and is known for his series of fights against Alexandre Franca Nogueira, from whom he suffered his only defeat ending his five year undefeated streak.
Tatsumi debuted on May 12, 1995, winning a unanimous decision against Magnum Kawamura at Shooto: Vale Tudo Access 4.
His undefeated streak would continue throughout the following year, including a decision win over Mamoru Okochi at Shooto: Reconquista 1 on January 18, 1997.
On March 28, 1999, at Shooto: Renaxis 1, Tatsumi fought Noboru Asahi to a three round draw, keeping his streak alive.
At VTJ 1999, Tatsumi faced Alexandre Franca Nogueira for the Shooto Lightweight Championship the fight ended in a draw.