In the novel, Mariko's appearance is never shown.
In the anime, Mariko is a young girl with short black hair, slicked back to show her forehead, and black eyes. She was shown wearing the female Shinyo Academy uniform.
Mariko seemed like a completely ordinary high school girl. She often spent time with Suiko, and was charmed by her mysterious personality. When the girl died, Mariko tried to also take her life, hoping she could follow Suiko to the "next world". However, after learning that Suiko was actually killed by Boogiepop, and didn't die of her own free will, she was unable to kill herself.
Mariko was a normal student of Shinyo Academy, who often spent time with Suiko Minahoshi.
Boogiepop Returns: VS Imaginator Part 1
While on the roof of Shinyo Academy, Mariko reminisced her time with Suiko, remembering the strange things the girl always said, that Mariko never really understood. She was ready to jump off of the roof, in order to be with the girl, when Boogiepop called out to her. He told Mariko that even if she jumped, she wouldn't get to be with Suiko again, because she didn't commit suicide, and was instead killed by him. Boogiepop then asked the girl if she still wanted to die, and, after looking down at the ground again, she realized that she wasn't able to jump anymore. Boogiepop then vanished as suddenly as he appeared, leaving the sad girl alone.
- The name Mariko means "real, genuine" (真) (ma), "reason, logic" (理) (ri) and "child" (子) (ko).
- Mariko's surname Komiya means "small" (小) (ko) and "temple, shrine, palace" (宮) (miya).