He is the karate teacher of the group. After a bumpy start, Tatsuya becomes Ayase's only confidant, but he is unable to expose Ayase's secret as the reason for his actions. Tatsuya tends to act silly trying to relieve someone's anger, so his efforts to ease the tension make Yuuri think he is mocking her. She decides that she can't rely on him. As a child, his father had bought off his karate teacher to give him a black belt. Everyone else bullied and envied him, thinking Tatsuya cheated and got away with it because of his father. His grandfather taught him Karate seriously, as a way to dispel the pain and anger of all the things he could not say. Naoto was the only one Tatsuya wanted to talk to in their university, even though other kids would follow Tatsuya only because of his family's reputation. When Naoto had to quit school, Tatsuya was miserable for the last two years without him around.
So when Naoto gets back into his life as Time Fire, Naoto chose not to interact with him. Tatsuya's father tries hiring the Timerangers for money and having Naoto as their leader. Tatsuya feared they would, but they reassure him they won't leave him for a power-seeking man such as his father. Tatsuya and Yuuri start to spend time doing little things together such as teaching her to make pancakes. In episode 39, everyone finally learns about Ayase's illness. When the others find out Tatsuya has been keeping the secret, Domon and Yuuri determine they must send Ayase back to the 30th Century. Tatsuya sticks by his friend, saying he hasn't given up and that is why he is still a Timeranger. In episode 41, Domon pairs Tatsuya and Yuuri together on a mission, under the theory that the pair will admit at last that they have feelings for each other. But since Domon wasn't remotely subtle about it, having been teasing them for some time, it seems to backfire.
Yuuri knows Tatsuya likes her, but she cannot admit to liking him back simply because she just doesn't know how to. Being pushed by Domon upset Yurri, and her being upset frustrated Tatsuya, who has done everything he can to not push her. Yuuri then got captured and Tatsuya was almost used as an instrument to kill her. But he was quick enough to discover the danger and free them both. Later, he tells her how horrible he feels even to think that he could have killed her. Later, Tatsuya finally meets Captain Ryuuya, and he learns that his becoming a Time Ranger was only what history had said, but that now he must take over the Asami Group and command of the City Guardians, because his father would die that very day. Tatsuya is forced to go and Captain Ryuuya takes his place as Time Red. He does so, even though his team member's refusal. Though his team refuses to accept this, Tatsuya leaves them at the Captain's command. He goes to the hospital for his father and is begged by businessmen to promise to stand for the Group.
While he waits to know his father's fate, he is miserably dispirited in his effort to change his own future. It is his mother who offers him comfort, and tells him details he had never known about his father. Such as when his dad was young, he had tried to win free of his family, but had been forced back and took the family name and power to new heights. His mother told him that she believes in both of them, and Tatsuya must never give up, any more than his father had. Eventually, Tatsuya can't withstand the conflicting demands on his heart and loyalty. When Takku comes to him begging him to help the team, he races off to the battle. When Captain Ryuuya tries to force him to turn back, Tatsuya tells him that history is already decided. Yuuri gives Tatsuya his Chrono Changer back, and he joins the group in battle. Tatsuya comes up with a crazy plan in order to defeat the G-Zord. After this, Tatsuya and Yuuri start to spend more time together, usually having serious conversations. When Yuuri sees nothing but her goal, Tatsuya is the only one able to go with her. When Don died, Yurri was nearly driven crazy with unfulfilled revenge and grief through it all.
Afterwards, Tatsuya behind having nightmares of his friends being sucked away into whirling vortexes. Who he is especially fearful for are Ayase and Yuuri. He decided they had to return to their own time, no matter what they want. He knew they will not go on their own and that they would stay and fight until time wiped them from existence, and he cannot let that happen. So he tricks them, traps them aboard the Time Ship, and sends them home. And after this, he races back into the fray. Takku had told them that Time Fire would die that day, and he will do everything possible to prevent that from occurring. A badly wounded Naoto was fired from the City Guardians and they wanted to take the V-Rex from him. Tatsuya drags Naoto to an emergency medical station, fighting through a horde of Zenitth. Tatsuya admitted to Naoto that he was relieved he didn't die. Naoto resented that Tatsuya had to the one to save him. Naoto gripped onto his V-Commander, Tatsuya asked him he was going to continue fighting. Tatsuya mentions to him that Yuuri commented that he can't see the end. Naoto responded by saying that one can't live only on power.
At the time, Tatsuya couldn't really grasp the significance of his statement. Naoto compares his running from death to Tatsuya's running from his family business. Tatsuya then finds free leeway to they are two peas in a pod. As the Zennith approach, everyone in the hospital run off. Before Tatsuya leaves, Naoto tells him he will go home if he lives. But Naoto doesn't live, Tatsuya finds him and is given the DV Defender by him with the final words to try to change Asami. The grief from Naoto's loss drives Tatsuya to the end as he fights. His friends return from the past and they stop the end of the world. He learns that the future has been changed. He has only a moment to say goodbye to each of them, when it is only he and Yuuri, and he confesses that he loves her. Tatsuya continues to live freely by himself living his life until he feels that he is ready to run his father's company. He lives on for Naoto. He hopes to one day see his friends again. He and Honami keep in contact and he will be there for her child. Although Yuuri is the team leader, Tatsuya is the driving force of the Timerangers, essentially acting as field commander during the battles.