Lemmy is half American, half Japanese - her full name is Lemmy Christopher Helen Miyauchi. She speaks Japanese with a stereotypical American accent, and often makes mistakes with the meanings of Japanese sayings. She also has a tendency to slip in English words during conversations when she has the chance. She also ends a lot of her sentences with "-ne" and overuses the word "fantastic". Near the end of To Heart: Remember My Memories she admits to Hiroyuki that she has always loved him and wants him to return to America with her so he can go to a good school with robotic engineering.
She is exceptionally tall and is the only major character who is taller than Hiroyuki. Her height, bust, blue eyes, blonde hair, and unusual personality is how her foreign blood is represented which is typical of many Japanese series that contain foreigners. Note that a picture shows that she has black hair originally.
Lemmy is also a member of the kyudo club (Japanese archery).