Matsuo is an esper affiliated with the Claw organization, specifically as a member of the elite 7th Division Scars subgroup, distinguished by scars earned challenging their leader. A vertical scar passes through his right eye. He typically wears a green striped collared shirt, black jacket, dark pants, and a belt holding multiple capsules containing captured evil spirits. His demeanor is generally calm but shifts dramatically when provoked, often unsettling others. He exhibits a peculiar fondness for his spirits, naming them with affectionate "-chan" suffixes like "Cookie-chan" or "Candy-chan."

During the 7th Division Arc, Matsuo confronts Dimple, attempting defeat using his spirit pets. After Dimple outsmarts him temporarily, Matsuo reveals his capacity to control multiple spirits and traps Dimple. He later attacks Mob and Reigen with spirits such as Gum-chan and Chocolate-chan, which Mob exorcises easily. Matsuo then unleashes his most powerful spirit, Candy-chan, a grotesque multi-headed entity. Reigen ultimately exorcises Candy-chan empowered by mass gratitude, leading to Matsuo's defeat by Dimple.

Following Claw's dissolution, Matsuo shifts to legitimate psychic work. In the Keiji Mogami Arc, he coincidentally partners with Reigen and Mob at the Asagiri mansion to exorcise the spirit possessing Minori Asagiri. Witnessing Mogami's power, Matsuo becomes determined to capture him. He assists Dimple in bypassing Mogami's mental barrier, contributing indirectly to Mogami's defeat. After Mogami is expelled, Matsuo seals him in a vial, dubbing him "Pudding-chan."

Matsuo makes a brief reappearance in the World Domination Arc. While Mob battles Minegishi, Matsuo drops his sticker-covered spirit container after being struck. A Claw subordinate ignores his warnings and opens it, releasing Mogami, which contributes to Minegishi's defeat.

Matsuo's primary ability involves capturing and controlling evil spirits. He weakens spirits using existing pets before sealing them in psychic-infused vessels, forcing their obedience. Spirits return to him after attacks, serving as offensive tools and defensive shields. Notable spirits under his command include:
- Cookie-chan: A multi-eyed, quadrupedal spirit exorcised by Mob.
- Gum-chan: A winged lizard-like spirit exorcised by Mob.
- Chocolate-chan: A life-draining octopus spirit exorcised by Mob.
- Candy-chan: His most reckless and powerful spirit, exorcised by Reigen.
- Pudding-chan: The captured Mogami, retaining independence due to immense power.

Matsuo's background includes defying Claw's leader, resulting in his scar. Post-Claw, his transition demonstrates a shift in goals, though his obsession with capturing powerful spirits remains consistent.