Rina was captured and held hostage by The Cyborg.
Rina is a young girl visiting Tokyo Tower with her mother, and she is taken hostage by The Cyborg and forced to attend a match on the top of the tower. Rina is later rescued by Mantaro Kinniku, who returns Rina to her mother and receives her gratitude for the rescue.
Rina is first seen in the waxworks museum. 
Rina is holding an edible treat, as she watches Mantaro act inappropriately with the mannequins, and she later watches as Mantaro proceeds to attack another mannequin. Towards the exit, after Mantaro risks being thrown out from the establishment, she offers him her treat to make him feel better. Rina and her mother join them in their tour. 
After The Cyborg emerges and defeats Gazelleman, Rina is taken hostage by him and dragged away to a ring on top of Tokyo Tower.  Rina is made to stand - with feet tied - on a very high beam of the tower, where she risks falling to the ground.  Rina watches the match from high above. Just as Mantaro seems like he might switch to the side of the Evil Chojin, Rina yells words of inspiration at him, which encourages him to fight again in earnest. 
After Mantaro wins the match, Seiuchin helps to untie Rina and deliver her back into the arms of her mother. And - as Mantaro gives her a thumbs up - she expresses her thanks to him for having saved her life. 
- In the anime movie, she was replaced by Kensuke