Rei Nasu/Plot

History
She joined Border as part of research on whether people with weak bodies can have healthy trion bodies. Half a year later, she showed her physical prowess on the battlefield.

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 Kuruma Unit. Later, she is seen strategizing with her entire team about how to deal with Kuruma Unit. 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 attack the three intruders. Wen Sō stays behind to face them. Nasu and Kumagai overwhelm her with their firepower and swordsmanship, respectively, so Wen Sō uses a smokescreen, and then transforms into Kumagai to deceive Nasu. She manages to cut off her arm. With the help of Kikuchihara's Side Effect, they manage to defeat their for.