Hideto Mitsu is a university student studying veterinary and zootechnical sciences. He possesses wavy light brown hair and brown eyes, typically dressed in a pale blue collared shirt over a white undershirt with gray pants. Ichiko Oda considers him good-looking. His personality demonstrates steadfast loyalty, responsibility, and meticulous attention to detail, coupled with tendencies toward anxiety and vigilance characteristic of an Enneagram Type 6. He exhibits an intense, obsessive fascination with Shiba Inus, particularly the canine protagonist, often staring intently at the dog while unintentionally overlooking Ichiko Oda's romantic interest.

He bears a striking resemblance to the historical figure Akechi Mitsuhide, sparking frequent comparisons and earning him the nickname "Mitsuhide." This likeness creates tension with reincarnated warlords, especially the protagonist who harbors lingering resentment over the Honnoji incident. Mitsu owns a pet chipmunk later revealed to be the actual reincarnation of Akechi Mitsuhide, establishing a complex dynamic where the chipmunk fears recognition while Mitsu remains oblivious to his pet's true identity.

Mitsu frequently visits the Oda household, where his childhood friend Tokiyoshi Honganji assists with chores. His veterinary expertise directly informs his interactions with the reincarnated dogs, and he serves as a human perspective bridging historical and modern contexts. He displays peculiar habits, such as exclusively drinking milk and offering it to both dogs and humans upon first meeting them, which Ichiko finds odd yet endearing.

His role expands through interactions with other reincarnated historical figures, including the repeatedly reincarnated scribe Ota Gyūichi, whose meat ironically ends up consumed by the dogs. Mitsu functions as a grounding presence amid the warlords' conflicts, though his obliviousness to Ichiko's affection and single-minded focus on the Shiba Inu fuel ongoing comedic situations within their social circle.