The exact backstory of Tatsu before the activities of the Foot Clan in New York is unknown. Tatsu came along with the Shredder to America, where he is completely devoted to him in his plan to conquer New York City by massive thefts. Tatsu is seen as The Shredder's second-in-command and personally oversees the entire youth center for the recruitment of Foot soldiers, while his master is away attending to other matters. Tatsu recruited and trained young runaways and street children as members of the Foot Clan and coordinated under the guidance of the Shredder theft in the city. He acts as the mentor of the Foot Ninjas.
However, his pupils generally feared Tatsu. He is shown to have a short temper, which could be discharged in a explosive fit of rage, physically abusing and punishing the Foot Clan for failure. He brutally injures and almost kills a young teenage Foot soldier named Shinsho (originally it was intended for Shinsho to die, in order to show the sheer brutality that existed within the Foot's ranks, but was cut and replaced with other dialogue: 'You'll be alright,' due to younger audience issues) for trying to calm Tatsu down and defend another Foot member.
Tatsu is shown to be un-waveringly brutal in both teaching and combat, as his rough methods for training Foot members. When one student proves adept at defending himself against Tatsu's attacks, Tatsu then bows to him, often the signal in martial arts that sparring has concluded. When the student bows back in respect, Tatsu dishonorably kicks him in the head and yells "Never lower your eyes to an enemy!" However, the student accepts his mistake and learns from it. Despite Tatsu's brutal reputation, he does not seem to concern himself with matters other than Foot business and training. When one boy bumps into him while the teenagers are carousing, the boy is in fear of Tatsu's anger. However, Tatsu is too concerned for such simple errors, who just brushes it off as an honest mistake and tells the boy, "Go, play."
When the reporter April O'Neil had too much unpleasant knowledge about the activities of the Foot, the Shredder ordered Tatsu to silence her. April was rescued from the Foot by Raphael and his family was made known, but he unknowingly betrayed them to the Foot Clan by having their existence known, and then the Shredder was openly hunting them. Danny Pennington, a young runaway, had sighted Michelangelo shortly afterwards in April's apartment and gave his knowledge to the Foot, whereupon Tatsu led a detachment of his Ninja against the Turtles. However, the Turtles and their friends escaped the trap with help from their new ally Casey Jones, which resulted in the destruction of April's apartment and antique store when one Foot Ninja sets it ablaze after electrocuting himself. Afterwards, Tatsu, in his anger over his failure, inadvertently almost killed one of his students, which sowed doubts about the motives of the Foot Clan in Danny.
When the Turtles after their exile in Northampton returned to New York to take the fight to the Foot Clan, Shredder gave Tatsu the order to kill the imprisoned Splinter. Casey Jones discovers him near the climax of the first film. When Danny and Casey made an effort to free Splinter, Tatsu got in their way. However, Jones comes out the better man, as he ultimately wounds and knocks an unsuspecting Tatsu unconscious with a golf club ko. Following this, Tatsu's fate remains ambiguous until the sequel. However, it is presumed he fled before the NYPD arrived to raid the Foot headquarters at the East Warehouse.
It is revealed that Tatsu managed to escape before the NYPD could find the Foot's original hideout at the end of the first film and meets up with the now vastly smaller Foot clan at their secondary base in a junkyard. The remaining members of the Foot gathered around Tatsu as he proclaims himself their new leader to lead the clan on behalf of the Shredder after his presumed death, just as the recently-thought- to-be-deceased Shredder returns. When it turned out that his master was alive he served him once more. Still second-in-command, Tatsu carries out the Shredder's first orders with ease; dispatching his best Foot Ninja to follow April O'Neil and securing a canister of a very effective mutagen from the chemical company TGRI, so that he could create mutant warriors to destroy the Turtles. His role is fairly minor compared to the first movie, although he remains unwaveringly loyal to his master and rarely leaves his side. Tatsu also kidnapped the senior scientists of the Institute, Professor Jordan Perry, so that he should support the Foot in its plans. He expresses a certain amount of joy in the idea of 'properly disposing of' the two new mutants created by Professor Jordan Perry's ooze; Tokka and Rahzar. In the film's penultimate battle in a night club where Vanilla Ice is performing, in his final confrontation with the Turtles, Tatsu is successfully 'shell-shocked', crushed between their shells, by the 4 turtles and stumbles away, unconscious. What happened to him and the rest of the Foot clan following their defeat, is unknown. It is presumed that since he was still there following the Turtles victory over Shredder, he may have been turned over to the NYPD for incarceration for his earlier crimes.
- The Japanese word tatsu means "dragon" referring to the mythological creature.
- Despite being played by a champion swordsman, Tatsu himself doesn't use any weapons in the films.