Yumi has never been the most social of people, she's often bitter and acts like she does not want to be wherever she is. Her shorter stature at 4'4 often has people confusing her for a child at a distance, but she will be quick to correct you in a rather sarcastic or cruel way. She was always a rather smart individual, easily getting good grades all the time, and is almost always seen sipping some coffee as she works on something. She's very much a fan of no-nonsense business.

Despite Yumi's distaste for most things, she oddly enough finds insects quite fascinating, and growing up she'd often be sitting alone in the grass observing the bugs as other kids played on the playground. This fascination would lead her into researching insects and even owning dozens of them as pets over the years. Others may have found her weird or gross, but she doesn't really care

She thought she could just live her life peacefully and alone, but one fateful encounter with a certain cat girl changed all of that. Sophie quickly grew attached to Yumi and wanted to be her friend, but Yumi wanted nothing to do with her, but Sophie kept persisting and eventually got her (or forced her) to meet her other friends, essentially assimilating her into the friend group forever. Yumi initially despised how obnoxious and weird some of them can be, easily criticizing them and their odd actions. But this eventually led to her meeting her soon-to-be boyfriend, Yoi, so I guess some things worked out in the end? Just don't tell that to Sophie.