Fun, fashionable, fiery and fiercely independent, Yumi is a mixed race gyaru girl who seems to have stepped straight out of the y2k-2010s era of style. She met Corrina while on a student exchange trip in middle school and two have been friends since, along with her younger sister Kimiko, keeping in touch online. Turns out they have relatives in the U.S. they'd visit occasionally and would get their cultural/language exposure built upon beforehand (helps with extra credit!)
Yumi would become a positive influence and an inspiration on Corrina, even teaching her about the different fashions and astethics from Japan and Korea's urban subcultures along with anime + manga, manwha, video game and music gossip. She'd even encourage Corrina in crafting fashion accessories and cosplay outfits, this helping her develop her own sense of style and self-confidence!
This would carry over into Yumi's personal life as someone who seeks to spread positivity and bring out the best in people and encouraging them to embrace their individuality via fashion/aesthetics, art and creativity or even just plain old encouragement!
The reason for this was because she and her sister both experienced discrimination and bullying due to their mixed heritage by some of their schoolmates and teachers, but did have a supportive older cousin (a gyaru herself) who taught them about fashion and aesthetics, and encouraged them to embrace themselves and their heritage, along with being their best selves the same way Yumi would do for Corrina.
She even has knowledge of automotive vehicles by style, brand and specs, along with some mechanical know-how for automotive care and matinence due to her father being a mechanic himself and a fan of the Fast and Furious movies along with his daughter. She ends up under Miko Nakadai's tutelage as apprentice mechanic for the Autobots when Japan becomes an open Cybertronian station with dad being contracted out of gratitude after he was saved by Jazz and his own team. Friends with Jazz and Blaster!
I'm still trying to flesh her and Kimiko out personality wise and not revert to stereotypes (playing with them is one thing) but use the positive aspects of some anime archetypes and expand upon how their multi-heritages both make them popular and ostracized at the same time in their society, which is why they both HIGHLY look up to Miko.
Extra notes:
-loves her younger sister dearly and understands/respects Caroline as a fellow older sister.