Rina and Nijimi have a two faced relationship. Rina, when she was the "Magical Hunter", killed Nijimi's best friend, Mikado Ikemata while her and Nijimi went out for karaoke. Nijimi was soon attacked by Rina after she found Mikado's body. Rina ended up fleeing from the fight after realizing she wasn't strong enough to beat Nijimi. Nijimi held a grudge against Rina ever since the murder occurred. Nijimi had plans to kill Rina for the sake of revenge. She even quit her career as an idol to try and find Rina.
Rina, after losing her home and stopped being the "Magical Hunter", enrolled in the same school that Nijimi (as well as Aya Asagiri and Tsuyuno Yatsumura) went to. As soon as Rina entered the classroom, Nijimi tried to kill her with her stick, before she could, she was tackled by Tsuyuno.
There are few moments in the manga and anime where the two are seen acting neutral towards each other. For example, in the manga, when everyone went to the beach, Rina and Nijimi weren't attacking each other during that time period.
When Nijimi died, she is shown to have a sad face. She admitted to Tsuyuno that she feels bad for her even if she tried to kill her which Tsuyuno replied that people like her should be the ones dead.
Rina and Tsuyuno met online. They decided to team up together and nicknamed a murderer who was killing Magical Girls to steal their sticks the "Magical Hunter". Then for unknown reasons, they lost touch. Tsuyuno thought that Rina was killed by the "Magical Hunter". Then after Tsuyuno has teamed up with Aya, Aya got confronted by Rina who was in disguise and trapped Aya in a box to kill her and steal her stick, Tsuyuno stopped time but was shocked when she saw that the 2 inside the box were not affected and she encouraged Aya to use her stick on Rina. Aya, who was hesitant to use her stick said that she might kill Rina but Tsuyuno assured her that she won't die since she stopped time, Aya then shoots Rina and got teleported to the place where Aya found the cat she cared for. Then Tsuyuno and Aya began to question Rina, which Rina didn't answer at first before getting threatened by Tsuyuno and finally answered and Rina collapsed because of overuse of the sticks' powers. After she recovered thanks to Kosame Amagai, the four decided to team up with the other Magical Girls which Rina joked to the two that she didn't kill them in their sleep for that reason. After they teamed up Rina and Tsuyuno became close friends. She also showed her appreciation as shown in Chapter 55.