Nijimi was a fair-skinned girl with cyan hair. Her attire consisted of dog ears on both of her twin tails, dog tail, a collar and a small dress.
Nijimi hid the effects of using her stick by dying her hair, wearing contact lenses, and using concealer on her emblem.
When she was a young child, Nijimi's family was behind on their house payments. She loved performing and said when she smiled, the people in the audience also smiled. The loan sharks suggested that they sell her just to pay their debt. Her father could not deal from the stress and committed suicide. Because of this event, Nijimi obtained her stick. She rewrote her family's memories to forget about her father, because they couldn't smile anymore. She narrated that she was saved by Mikado Ikemata and resets everyone's memories who were involved that day and erased the loan sharks' memories, shortly after that she got accepted to Dog Play without her stick.
She seemed to be cheerful and naive. She was also fearless but when talking about Mikado and Rina she changed from being a sweet idol to an obsessed person with a strong desire of revenge in seconds. She must have also like attractive men since she was attracted when she first saw Kaname Asagiri.
She also had a temper that she has a hard time controlling.
By wearing the magic panties given to her by Nana, she was able to take control over people's minds by giving them direct orders.
- She might be a good artist as she drew Rina Shioi's face (which is technically Saki Shizukume's face) in a matter of seconds, but this might be because she was so focused on getting revenge on her.
- If Saki encountered Nijimi, she seems to have been mistaken for Rina and was killed first.
- She had a habit of biting her nail when enraged.
- She was the 2nd person to be killed by Kaname Asagiri. The first person that was killed by Kaname is Keisuke Naoto.
- Her design must be inspired by Fukumoto Tsukune, a character of Mahou Shoujo of The End.
- She resembled a Chihuahua in Dog Play.
- She was the favorite member of Sakura Sakaki.
- She liked tapioca milk tea, apples and dogs. And disliked cuisine.
- Her seiyuu (Yu Serizawa) sings the ending song in Episode 3 of the anime.
- Nijimi hid the effects of using her stick, dying her hair, wearing contact lenses, and using concealer on her emblem. Then she said where she bleeds is a secret, meaning she might bleed from her female genitalia when using her stick.
- However, in Chapter 103, it turns out that the bleeding part due to use on the stick is an ass.
- She is the first main character to be killed in the series.
- She has a diary.
- The 虹 in her name means "rainbow", while the 海 in her name means "ocean".
- In the manga, she made faces similar to Explode・M / Ribs from Mahou Shoujo of The End.
- Her stick's power can control the minds of unconscious people, this was shown when she was about to control Rina while she was in a coma.
- In Spanish playing cards, the spade ♤ means the military, that bring us the idea of dominance, power and authority, which quite matches her stick's ability, Mind Control.
- Although it's name wasn't revealed, she has a single.
- Her character has some similarities with Miku Izayoi, a character from the Date A Live series.
- Her birthday is on July 5th.
- Along with Sakura Sakaki, Nijimi's horoscope is Cancer.