Tetsu is Karada's classmate and one of her closest friends. Tetsu is quite tall, joking that he is sometimes mistaken for a high school student. It is implied that he likes Karada - when Karada "went missing" after she became older, he ran all over town to find her.
In the manga his role is much bigger than the anime, and his relationship with Karada more problematic.
(Manga)
Shortly after she turned into an adult, Tetsu tried to make Karada give her a hand job. This scars her horribly, and the two don't talk to each other for a long time after. It's for this reason that he wishes to find the wishing stone so that Karada can return to being a kid again. He does this with the aid of Shouko, the only person who talks to him after the incident.
