Isumi Yayoi is one of the main heroines in the original Kimi ga Ita Kisetsu and its 2011 remake version. She also appeared in Muv-Luv Alternative Chronicles Inheritance. She is the eldest of Isumi sisters. Landlady of Narumi Takayuki in Kimi ga Nozomu Eien.
Within the Alternative universe, She works for the Imperial Japanese Government in the Home Ministry, in a division similar to that of Yoroi Sakon concerning the internal affairs of Japan.
- Yayoi has the largest bust (B98/W56/H86) compare to her sisters.