Hirano Hasegawa, a 17-year-old female member of the police unit Genius Four, bears the Japanese name 長谷川 平乃. Her surname Hasegawa signifies "long valley river" while her given name Hirano means "flat from". She possesses black hair, brown eyes, a height of 1.54 meters, and a weight of 44 kilograms, with blood type B. Characterized by politeness, she exhibits martial arts proficiency—notably employing a sleep-inducing karate chop technique. Off duty, she trains at a dojo, sparring against opponents substantially larger than herself. Hirano appears in franchise installments including the summer special, second season, spin-off "Futari wa Milky Holmes", and the movie.