A member of the 4th Mobile Investigative Unit (MIU). He is Ai Ibuki's partner and holds the same rank of Sergeant. One half of the Unit 404 crew. Originally from the First Investigation Division, he was transferred to MIU due to various circumstances. He possesses calm judgment and observational skills that allow him to see several steps ahead. He specializes in steady, grounded investigations, meticulously gathering evidence. While he is an exceptionally elite detective, he occasionally plays along with Ibuki's antics. Though often swung around by Ibuki's polar opposite personality, when the situation calls for it, he can be even more reckless and uncontrollable than his partner. Usually, he appears cool, detached, or even a bit lazy, but he becomes passionate and hyper-focused during investigations. At times, his expressions and words carry a sense of deep melancholy. Due to the Doughnut EP incident, he developed a fear of round objects with holes in the middle. Since meeting Ibuki, he has started to smile just a little bit more. Attire: Usually wears V-neck or clean-cut T-shirts under a jacket with the sleeves rolled up. Wears standard trousers and shoes. His partner Ibuki calls him "Shima," or playfully "Shima-chan." Height: Slightly shorter than Ibuki. Speech style: Uses masculine, assertive forms like "...janai ka," "...daro," and "...da." He can be foul-mouthed at times and has a cheeky side, occasionally sticking his tongue out.

A member of the 4th Mobile Investigative Unit. Rank: Lieutenant. One half of the Unit 401 crew. His former partner was Yoshito Kokonoe, but he is now partnered with the rookie Takanori Kariya. Image breed: Bulldog (fighting dog). A veteran MIU member who once partnered with Shima. He has a boisterous personality, living by the motto: "If someone takes the high ground, take it back." Speech style: Rough and masculine, using forms like "...jane-ka," "...daro," and "...janai ka?"

Formerly served concurrently as the Captain of both the 1st and 4th Mobile Investigative Units. Currently serves as the Chief of the West Musashino Police Station. Rank: Superintendent. Image breed: Borzoi (hunting dog). A highly capable officer who became the first female Captain of the 1st MIU after serving as a station chief; she is also the one who proposed the four-unit MIU system. She was in the same squad as Kazumi Shima during their time in the First Investigation Division and still maintains strong trust in him. Even after her transfer, the MIU4 members still call her "Captain." Only Jinba calls her by her surname, "Kikyo." Speech style: Polite but firm feminine speech, using forms like "...janai no?" and "...ne."

As a high schooler, he was involved in a false reporting incident in the West Musashino jurisdiction, but he reappears here as a rookie member of the 4th MIU. Having joined the very unit that once pursued him, he now partners with the veteran squad leader Kohei Jinba. He is working toward his dream of becoming a detective. While he occasionally faces criticism regarding his past, the 4th MIU always has his back. He is sharper than before. His speech is intelligent and polite (keigo), but he still has a cute side.