Lemmy Christopher Helen Miyauchi is a 16-year-old half-Japanese, half-American character born in California on December 21. After relocating to Japan, she re-enrolled as a student in the same academic year as Hiroyuki Fujita. Her family consists of parents George and Ayame Miyauchi and siblings Cindy and Michael, with Lemmy as the middle sister.

Physically distinctive at 174 cm—taller than Hiroyuki—she has blonde hair typically styled in a ponytail with spiky bangs and blue eyes. Her measurements are 92-59-86 cm, contributing to a slim yet prominent figure.

Lemmy exhibits a loud, boisterous, cheerful, and energetic personality, often appearing airheaded or carefree. Despite occasional linguistic errors, she displays unexpected wisdom and insight. Her kind-hearted nature makes her consistently supportive of friends, embodying a deredere and openly romantic disposition.

Raised in California, she speaks Japanese with American influences, frequently inserting English phrases and mispronouncing Japanese words. She overuses "fantastic" and confuses idioms, resulting in humorous exchanges. Her background includes multilingual capabilities.

She participates in her school's kyudo club, demonstrating exceptional accuracy against moving targets but struggling with stationary ones, aligning with her broader interest in hunting.

A significant background detail reveals her as Hiroyuki's unrecognized childhood friend. During her earlier years in Japan, she dyed her hair black to avoid standing out as foreign, explaining Hiroyuki's initial lack of recollection. She retained long-held feelings for him.

In the storyline of "To Heart ~Remember My Memories~", Lemmy confesses her affection to Hiroyuki. Facing an imminent return to America, she invites him to accompany her to study robotics, but he declines.

Her family connections include part-time work alongside her siblings, often in waitstaff roles. She is also a pet owner.