Hayakawa functions as the personal butler to the Minowa family, exclusively dedicated to Hijiri Minowa. He presents as an elderly male with grey hair and grey eyes, though a singular source observes an unexplained resemblance in his appearance to a girl during their youth. His core duty entails operating a Ducati 750SS Imola Replica motorcycle equipped with a sidecar, consistently documented as his assigned vehicle for transporting Hijiri prior to her obtaining a riding license.

A defining display of his loyalty occurs during a "chicken" game initiated at Hijiri's command. Hayakawa accelerates directly toward opponents without faltering and deliberately drives the motorcycle and sidecar into a river to realize her wish for rebellious action. This incident exemplifies his willingness to execute Hijiri's requests irrespective of personal danger or practicality.

Following Hijiri reaching the legal age for riding, she secures a moped license and later acquires a Ducati 1199 Panigale S. Hayakawa's role consequently evolves from direct transportation to supporting her independent riding activities.