Midori Tooyama attends school alongside main characters Tatsuya Asagiri, Feena Fam Earthlight, and Natsuki Takamizawa, sharing a close friendship with Tatsuya's younger sister, Mai Asagiri. She possesses distinctive green hair cut to neck length and brown eyes. Her height is 1.57 meters, with measurements of 84-56-86. Her birthday is February 10, and she has blood type B.

Midori exhibits high curiosity and enthusiasm. Once her interest is engaged, she demonstrates a strong desire to understand things in exhaustive detail, showing persistent focus. This trait contributes to perceptions among peers of her being carefree or overly excitable. She displays determination and diligence in pursuing her interests, particularly her passion for playing the clarinet, which secured her the position of first clarinet in the school orchestra.

She expresses a consistent desire for attention and recognition from Tatsuya. Notably, she wishes to receive the same casual nose-pinch gesture he gives to others like Mai or Natsuki, though he consistently declines to do so to her, underscoring her unrequited interest.

Within official media, her narrative role varies. In the anime series, she primarily serves as a secondary character providing comic relief through her energetic personality. However, in expanded materials related to the visual novel source, particularly newer console versions, she features more prominently as a potential romantic interest for Tatsuya, offering a different narrative pathway. Her background beyond school activities and orchestra participation remains unspecified.