Kokoro Akechi commands the police investigation unit Genius Four, specializing in cases linked to the Gentlemen Thieves. Her name honors the fictional detective Kogoro Akechi from Edogawa Ranpo's works, embedding her within a detective character legacy. Her surname Akechi signifies "bright wisdom," while Kokoro translates to "small clothing."

Thirteen years old, she stands 139 cm tall, weighs 30 kg, and possesses blonde hair. Kokoro relentlessly proclaims her intellectual dominance, boasting an IQ of 1300 and claiming graduation from Harvard University at age 13. She exhibits a bossy attitude, particularly towards the Milky Holmes detective agency, whom she derides after their loss of special abilities called Toys.

A recurring comedic trait sees her striking Sherlock Shellingford with a golden mask whenever addressed informally as "Kokoro-chan." This mask subtly evokes Kogoro Akechi's adversary, the golden-masked Fiend with Twenty Faces.

In "Gekijōban Tantei Opera Milky Holmes: Gyakushū no Milky Holmes," Kokoro and Genius Four engage in a three-way conflict against Milky Holmes and the Thieves' Empire. Alarms disrupting a study tour trigger the battle, where both sides deploy their Toys until Milky Holmes loses their abilities after a lightning strike. Throughout the film, Kokoro consistently maintains her self-proclaimed genius status and confrontational stance towards Milky Holmes, reinforcing her established role as the movie reunites franchise characters.