Kazuichi Arai 荒井一市

Arai Kazuichi is the temporary homeroom teacher for the gang's class. He is nicknamed Pin and always is called that way (except Sawako who obeys the formalities and still calls him Arai-sensei). (The previous homeroom teacher had been said to be sick after he made Sawako do his work during the summer holidays.)

He is a great fan of baseball as well as the school baseball team's coach. He used to be part of Shouta Kazehaya's father's league team, so he has known Shouta since when he was young. He had once said that he likes to 'interrupt' people. He nicknames Kazehaya and Sawako's found-beside-the-river puppy Pedro Martinez.