Kokoro Akechi leads the police investigation unit Genius 4, abbreviated as G4. Her character directly echoes Edogawa Ranpo's detective Kogoro Akechi through surname and profession. She consistently exhibits a bossy, condescending attitude toward the Milky Holmes agency, especially after they lose their special Toys abilities. A recurring comedic trait sees her strike Sherlock Shellingford with a golden mask when addressed informally as "Kokoro-chan." She frequently boasts of intellectual feats, claiming Harvard graduation at age 13 and an IQ of 1300.

In the spin-off *Futari wa Milky Holmes*, Kokoro mentors the Feathers detective duo, Kazumi Tokiwa and Alice Myojingawa. This role leverages her investigative experience and contrasts with her earlier Milky Holmes antagonism. Her guidance through cases demonstrates development beyond initial rivalries and reveals previously unacknowledged professional competence as she actively supports the Feathers' growth.

Her investigative methods and police duties remain unwavering. She maintains law enforcement authority, prioritizes formal procedures, and often clashes with unconventional detective approaches. Her character design and traits—including the golden mask for comedic effect—persist throughout all appearances, though her role expands to guide newer characters in later narratives.