Yayoi has long black hair reaching down towards her chest and back with blue eyes. She is seen wearing a thin-strapped pale grey top with equally as thin yellow bra straps and pink hot pants.
She is candid around her brother thinking nothing of entering his room and throwing his boxers at him to flatly telling him that he sucks on guitar or that he is late in making them both dinner. Often acting irate around him whether he is not listening to her, she softens her demeanor when around others particularly Akihiko.
She grew up with her brother where Ritsuka remembers in the sixth grade, Yayoi was sat in a uniform eating a blue ice lolly watching the TV whilst Ritsuka practiced on the guitar. She does not hide her opinion that he sucks at it.
Yayoi enters Ritsuka's room to throw his boxers at him that were in her laundry, before asking about his band practice with Akihiko in mind. Later she tells Ritsuka he is late home and gets him to prepare pizza for dinner.
From Japanese: The meaning of Yayoi is "spring". Yayoi is generally used as a girl's name. It consists of 5 letters and 2 syllables and is pronounced Ya-yoi.
- She owns a pink-colored phone.