During his school years, he was in a small gang of high school kids. When his gang members came back with Ren, he was not pleased with him. One of his gang members started to empty out Ren's school bag when his deck box came out. When Tetsu asked what it was, Ren explained as a card game called Cardfight!! Vanguard, a popular game that is taking the world by storm currently. Tetsu was looking at the cards when Ren noticed that the cards were glowing a bright rainbow like color around them. Ren ran to him and told him to play the game. At first, Tetsu would turn down Ren's offers to play the game whenever he came to the hideout. Evenually, he gave in and took Ren's offer of playing the game. They fought on the rooftop of the school. When Tetsu lost, he asked Ren to battle him again until he finally wins in the end. Tetsu wanted to battle more, but Ren told him that it was getting late. That was when Tetsu noticed that they spend the whole day playing this game and he decided that this game is worth playing.
Personality
He is the more quiet member of his team, only talking when he needs to. Although he is tall and appears to be intimating, he is actually a gentle and kind person. He cares very much for his teammates and always help them when can. When it comes to children, he would be shown answering their questions about Cardfight and doesn't mind helping them out with their decks. Like one time he offered some opinions on Emi's choice of Grade 3s for her deck while commenting on Kamui's play style. When cardfighting though, he can be absolutely relentless and will call his opponents out on their weakness if they are not up to the level they should be.