|Japanese name:||荒井 一市|
Birthdate: 25th July
Height: 193 cm [6'4"]
Weight: 88 kg [194 lbs]
Life philosophy: "I'm always right."
Arai is the temporary homeroom teacher for Sawako's class, taking over when the previous homeroom teacher became sick during the summer holidays while Sawako was helping him. He is nicknamed "Pin" and always is called that way, except Sawako who obeys the formalities and still calls him Arai-sensei. The reason he is called "Pin" is explained in the after-notes of Volume 1. Pin is a great fan of baseball as well as the school baseball team's coach. He used to be part of Kazehaya's father's league team, so he has known Shouta since when he was young. A loud and eccentric man prone to believing the silliest things, Pin apparently enjoys interrupting people. He had nicknamed the puppy that Sawako and Kazehaya found by the river "Pedro Martinez" after the legendary baseball pitcher. (Sawako suggested it be named "Maru", and that is its real name.) A running gag through the series, despite being a teacher he is prone to actions that are more suited to a teenager, such as eagerly running to the bathroom when he heard about a fight yet became depressed when Sawako and her friends were making up rather than fighting. He and Ayane tend to run into each other a lot, often bickering loudly as they walk away, though on rare occasions he will give her advice (though comically ends in him ruining the moment to praise himself). He also has a false impression that Sawako is an exorcist.