Masumi Yodogawa is an Oni and the commanding officer of the Oni Agency’s Patrol Unit in Nerima, Tokyo. Serving as the captain of the Nerima Ward Reconnaissance Unit, he is recognized for his stealth, analytical thinking, and ruthlessly efficient leadership. His background includes time as a student at Rakshasa Academy, where he was classmates with Naito Mudano and Kyoya Oiranzaka. Kyoya often addresses him by the nickname Massu, a label Masumi himself dislikes.

In terms of personality, Masumi is blunt and direct, frequently speaking his mind without concern for how others might perceive him. He maintains a calm and composed exterior, adhering to a personal creed of keeping a poker face, and his words and actions can come across as cold. Despite this, he carries a genuine concern for his comrades and is affectionate toward the members under his command, even if he is strict with them. He has a foul mouth but backs his words with conviction. He possesses advanced intellect and a cautious nature, always considering multiple possibilities and excelling at gathering and analyzing information.

Masumi’s primary motivation stems from a deep sense of duty and loyalty to the Oni Agency and to those he fights alongside. He believes strongly in the value of reconnaissance work and the determination required to serve on the front lines. He is driven by a desire to protect others and to ensure that no effort is wasted, often putting his own body on the line to achieve his objectives. He holds that as long as one does not break their heart, their chances are never zero.

Within the story, Masumi plays a key supporting role as a seasoned field commander. He is responsible for overseeing reconnaissance operations in Nerima and frequently works alongside his vice-captain, Dokaori Namiki. He becomes involved in events surrounding the main characters when Mudano and his students arrive in Nerima. Masumi assists in locating and rescuing Jin after he is kidnapped, using his abilities to infiltrate the enemy hideout. He also takes on a direct instructional role for the younger members, teaching them the realities of reconnaissance work and encouraging them to maintain a sharp, unyielding mindset. During a confrontation with a rampaging Shiki, Masumi intervenes to buy time for others, deliberately drawing Shiki’s attention despite the danger. In that encounter, his right ankle and below are blown off, a severe injury that nearly proves fatal. He is saved by Mudano and later treated by Kyoya, allowing him to recover and continue his duties.

Key relationships include his bond with Mudano, whom he has known since the academy and treats with a familiar, teasing attitude. He respects Kyoya as a capable ally and former classmate, despite disliking the nickname Kyoya uses. He maintains a strong working relationship with his vice-captain, Namiki, and acts as a mentor figure to younger reconnaissance members.

Masumi’s notable ability is a power activated by licking his own blood, which renders him completely invisible for up to ten minutes. This effect also applies to anything he is wearing, allowing for full concealment during missions. When he first developed this ability, it only lasted thirty seconds, but through effort and experience he extended its duration significantly. He has suffered torture during a past mission, and his body bears scars from that experience. He fights with a combination of stealth, tactical awareness, and a willingness to endure harm for the sake of the mission, making him a reliable and formidable operative on the front lines.