Kokoro Akechi leads Genius 4, also known as G4, an elite police investigation unit. Her character is inspired by the classic detective Kogoro Akechi from Japanese fiction. She is a young girl who claims to have graduated from Harvard University at the age of 13 and often boasts an IQ of 1300. Her personality is defined by intense pride and bossiness, and she looks down on the Milky Holmes detective team, especially after they lost their Toys. She is particularly annoyed by Sherlock Shellingford calling her by the familiar name Kokoro-chan, a transgression she punishes by striking Sherlock with a gold mask. Although she is easily distracted by her own high opinion of herself and is prone to losing her temper, she is genuinely sharp and takes quick, decisive action in dangerous situations. Her peers, such as Tsugiko, recognize that her leadership is a fortunate asset during crises. The motivations that drive her center on her identity as the head of G4 and her desire to assert her unit's superiority and prove her genius. In Futari wa Milky Holmes, her role shifts from being a rival to the main characters to becoming a direct mentor for the Feathers, the detective duo of Kazumi Tokiwa and Alice Myojingawa, applying her investigative experience to guide them. Her key relationships involve her adversarial dynamic with Sherlock Shellingford, her authority over the members of G4, and her mentorship of the Feathers. Her notable abilities include a claimed genius-level intellect backed by sharp observational skills and the authoritative leadership that allows her to act decisively in high-pressure situations. Her development across the narrative sees her evolve from an arrogant antagonist into a more responsible and respected mentor figure, revealing hidden depths of seriousness and secret maturity beneath her small stature and inflated ego.