Kokoro Akechi leads the police investigation unit Genius Four (G4), specializing in cases involving the Gentlemen Thieves. At 13 years old, she stands 139 cm tall and weighs 30 kg. Her appearance features blonde twin tails with spiky bangs and blue eyes, complemented by a uniform of a miniskirt, thigh-high stockings, boots, a necktie, and an armband.

She exhibits a bossy and serious personality, frequently disparaging the detective group Milky Holmes after their loss of supernatural Toys. Kokoro consistently touts her intellectual achievements, asserting she graduated from Harvard University at age 13 and possesses an IQ of 1300. Her name references the fictional detective Kogoro Akechi, aligning with the series’ detective-fiction homage theme.

A defining rivalry pits her against Sherlock Shellingford, Milky Holmes’ leader. Kokoro reacts violently whenever Sherlock addresses her informally as "Kokoro-chan," striking her with a golden mask—a recurring gag. She occasionally deceives Milky Holmes, such as falsely pledging to restore their Toys.

Across media, Kokoro maintains her role as G4’s leader without significant backstory expansion. Her appearance in the spin-off *Tantei Kageki Milky Holmes TD* documents no substantive evolution in her character arc. Her interactions persistently focus on police investigations and antagonism toward Milky Holmes, preserving her core traits and relationships.