Masato Inohara is a core member of the Little Busters and serves as the roommate of Riki Naoe. He is the tallest character in the series, with black spiky hair, blue eyes, and a signature red headband. His well-built physique reflects his single-minded dedication to physical training and improving his muscle mass. Before joining the Little Busters, Masato experienced a difficult childhood marked by bullying. In response, he devoted himself to strength training in order to never be victimized again. Although he succeeded in building an imposing body, the pursuit of physical power left him emotionally isolated and without a clear sense of purpose. His life changed when Kyousuke Natsume challenged him to a fight, defeated him, listened to his story, and then invited him to join the Little Busters. That invitation gave Masato a sense of belonging and companionship he had never known.

Masato is often portrayed as muscle-obsessed and somewhat dense, leading others to affectionately call him the lovable idiot. Beneath that exterior, however, he is one of the most reliable and loyal members of the group. He is open in his fondness for Riki and is always ready to support his friends, either by participating enthusiastically in the group's antics or by stepping in when someone needs protection. His heart is described as soft as tissue despite his steel-like body. He has a constant friendly rivalry with fellow member Kengo Miyazawa, though their bickering usually only takes place when Kyousuke is present, suggesting their conflicts are partly performative and rooted in camaraderie. His relationship with Rin Natsume is more contentious, marked by frequent arguments and occasional physical scuffles; Rin often calls him a muscle-brained idiot and deleted him from her phone's address book, but their clashes contribute to the group's lighthearted dynamic.

Masato is deeply aware of the repeating events in the artificial world and what lies ahead, yet he always acts as his true self, never faltering or letting his awareness show. He supports Kyousuke's plan to strengthen Riki and Rin to overcome the real-world tragedy, even though he is reluctant to put them through hardships. When it truly matters, he sides with Kyousuke. During the Refrain arc, Masato temporarily distances himself from the group in an effort to prove his own strength. Haunted by an old defeat, he falls into a confused state and begins to perceive everyone around him as versions of himself, reflecting his inner turmoil. After being defeated by Riki and Rin, he recalls his past of being bullied, his turn to strength training, and his lonely life before Kyousuke's invitation. Riki echoes Kyousuke's earlier gesture by inviting Masato back into the group, which he accepts. This moment allows Masato to understand that strength lies not only in muscle but in friendship.

Masato possesses immense physical strength, the result of years of obsessive training. He can lift heavy objects, deliver powerful blows, and even scale a vertical wall, as shown in certain routes. His greatest notable ability, however, is his unwavering loyalty and willingness to sacrifice himself for his friends. In the real world, during a bus accident on the school excursion, Masato shields Riki with his own body, saving his life and sustaining serious injuries in the process. That act solidifies his role as both a physical and emotional pillar of the Little Busters. His growth is marked by his transition from a lonely boy seeking strength to a dependable friend who finds true meaning in protecting and supporting those he cares about.