Rei Nasu/Plot

Background
Nasu joined Border approximately two years before Yūma Kuga and Chika Amatori as part of a research on whether sickly individuals will produce healthy trion bodies, becoming a proficient Shooter within the following six months. At some point she asked her cousin Narasaka to mentor Hiura.

B-Rank Rank Battles Arc
She is first seen together with Kumagai on her house, chatting with Shiki through a computer about the upcoming rank battle with Tamakoma Second and Suzunari First. Later, she is seen strategizing with her entire team about how to deal with Suzunari First. She notes that Murakami was their biggest threat.

During the battle, she starts off on the eastern half with Osamu, Chika, Kuruma, and Betsuyaku. She pursues Osamu while blocking attacks from Betsuyaku and Kuruma and attacking them. After Chika destroys the bridge, she changes her plan such that she would eliminate all her opponents on her side. She manages to defeat all 3 of her opponents, but runs out of trion before she can fight Yūma. She regrets not being able to win for her team, but her team assures her that they did well.

During the Galopoula Invasion, she and Kumagai confront the three intruders, and Wen Sō stays behind to face them. Nasu and Kumagai overwhelm her with their respective firepower and swordsmanship, and Wen Sō uses a smokescreen to counter them. She then disguises as Kumagai to deceive Nasu, and manages to cut off her arm. With the help of Kikuchihara's Side Effect, they manage to defeat her.