Kokoro Akechi commands the Genius 4 (G4) police investigation unit in the Yokohama District. She wields authority with a dismissive sneer toward the Milky Holmes detectives after their loss of special Toys, openly mocking their fallen status. A signature comedic ritual sees her strike Sherlock Shellingford with a golden mask whenever addressed as "Koko-chan." She constantly trumpets claims of intellectual supremacy, insisting she graduated from Harvard University at age 13 and possesses an IQ of 1300.

Her design features blonde hair styled with spiky bangs and twin tails, piercing blue eyes, and a notably petite stature standing 139 centimeters tall and weighing 30 kilograms. She typically wears a police uniform: a miniskirt, thigh-high stockings, boots, a necktie, and an armband.

Within the *Tantei Kageki Milky Holmes TD* narrative, Kokoro investigates a series of song thefts targeting idols. When super idol Marine Amagi loses her hit song "Kiseki no Uta," Kokoro finds herself collaborating with the Milky Holmes team to solve the case. Her role remains unchanged: she persists as a police investigator, maintains her contempt for Milky Holmes, and employs her golden mask gag against Sherlock. She is the only Genius 4 member featured this season.

Her portrayal across all official media consistently emphasizes her function as a comedic antagonist defined by exaggerated boasts of genius and her established dynamic with the protagonists.