Tetsuya Sendo is a voluntary member of the Kasanoda Syndicate. Previously, he was the heir to a rival syndicate, but he disagreed with how the syndicate ran its business. After a final confrontation with his father, he ran away from home. Scared and alone, he sat on the sidewalk in the rain wondering what to do. it was here that he met Ritsu Kasanoda, who held out his umbrella to shield Tetsuya from the storm. Tetsuya instantly understood the kind of person that Ritsu was and joined the Kasanoda Family Syndicate. Ritsu considers him his closest friend.
Tetsuya's age is unknown, though he appears to be rather young. He has light skin and light brown hair held in a thick, high ponytail that reaches just below his shoulders, round grey eyes and a rather sweet face, giving him a rather feminine looking appearance. He has a bandage on the side of his fact which, it may be speculated, conceals a tatoo identifying his original family. He typically wears a baggy green shirt and loose trousers, and has several piercings in one ear. Tetsuya is and easy-going and loyal person, except when people he cares about are threatened, his personality than displaying a more ganster-ish affect. In the anime, Tetsuya is the only member of the Kasanoda syndicate who is not terrified of Ritsu, though he is occasionally surprised. In the manga, he is frightened of Kasanoda, just like the other mobsters.
Tetsuya starts out in the series as a housekeeper for the Kasanoda syndicate after being rescued from the streets by Ritsu, who seems to feel sympathy for the younger man. Because of their unique history, Tesuya has a habit of confronting Ritsu, which angers the other members of the syndicate.
Tetsuya arrives at Ouran Academy to deliver Kasanoda his umbrella, only to walk in on him wearing a cat-maid outfit. This humiliates Kasanoda and he scares Tetsuya off. While departing Ouran, Tetsuya spies two thugs of the Sendo syndicate and threatens them to stay away from Kasanoda, who inadvertently observes the exchange. Tetsuya then reveals that he is the son of the mob boss of the Sendo syndicate, but left home a year ago due to differences of opinion with his father's methods. Tetsuya also informs Kasanoda that he and the rest of the Kasanoda gansters are aware of Kasanoda's true nature and that he has 'fallen for his character' and desires to be more like him.
It is Ritsu who rescues Tetsuya from the streets with a simple offer of an umbrella against the rain. Tetsuya instantly understands the kind of person that Ritsu is and swears allegiance to the Kasanoda Syndicate. Ritsu considers Tetsuya his closest friend.
- (To Kasanoda syndicates about Haruhi) Oh yeah, I see them hanging out together a lot. Fujioka does have an unusually cute face - I mean, for a guy.
- (To Kasanoda in the new fashion style) Young lord, what the hell's going on? Something happen at school today?
- (To Kasanoda in the cat maid outfit) Sir, it's no big deal. You can do whatever you want in your spare time.
- (To thugs from the Sendo syndicate) Don't you get it? The reason I left was because I was sick of hanging out with the likes of you! Get lost; you hear me?