Masato is a member of the Little Busters, and is Riki's roommate. He has a particular fondness for Riki, which he is more than willing to express out aloud. He loves to work out and improve his muscle mass. His rival is Kengo Miyazawa, fellow member of the Little Busters. In Refrain, he left the Little Busters, thinking Riki is not strong enough to led the group. After Riki questions him about what he is planning to do after leaving the Little Busters, Masato answers that he wants to prove that he is the strongest, and when he thinks about how he was defeated on May 13 and his will to become the strongest, it leads to his rampage, when everyone in his point of view becomes Masato, which in truth is his state of confusion on what he is living for. After he is defeated by Riki and Rin, Masato has a flashback about his past. He was bullied when he was little; he needed strength not to be bullied so he trained his muscles to be number one, but at the same time he felt lonely, and later wonders about what he is living for. One day, Kyousuke challenged him to a battle and he is defeated. After listening to Masato's story, Kyousuke invited Masato to the Little Busters, and Masato felt that his battle was over as he now had friends. Riki invites Masato to the Little Busters the same way Kyousuke did, and he agrees to join again. During the school excursion, he saves Riki in the real world during the bus accident.
Unsurprisingly, Masato has the highest starting strength and stamina points out of all characters in the game. However, his all other attributes are average or below-average, which play a more important role on the mini games. His low concentration and judgment points mean he is more likely to make tactical errors during the baseball game. Depending on the choice the player makes during May 17, however, his skills during the baseball game can be increased further, though he still has a tendency on making mistakes.