He has short reddish brown hair.
He loves high school girls. He makes no attempt to hide this either. However, he never actually touches any of the girls, just acts overly friendly towards them and overly cold towards the guys. He often demands that any guys with girlfriends (mainly Miyamura and Sengoku) break up with them, so that he can have them instead. Any time he is with only male students, he constantly bemoans the fact, loudly asking why they, and not some girls, are there. He also does not tend to remember the names of his male students, saying that he has no need to learn useless information. Many of Yasuda's female students also like him as well, thinking he's a cool, young, good looking teacher who's kind to them. Many of them like to visit with him in the counseling room.
Terajima acts very hostile towards Yasuda. Her main goal is to protect the girls (and some of the guys) from Yasuda's advances. However, even when there aren't any girls around, she still is very hostile towards Yasuda, thinking him a lolicon teacher. Yasuda usually protests her unfair characterizing and treatment towards him, though in rare occasions, when Terajima is excited about something, Yasuda can treat her just as bad and knock her down a peg.
Yasuda and Nakamine both attended Katagiri High School together, though Yasuda doesn't remember Nakamine. Now that they are both teachers, they interact in a very similar fashion as they did in high school, with Yasuda somewhat irritated at Nakamine, and Nakamine just laughing off everything as a joke.