|“||I don't know how many matches we'll have left. So... let's take the top! This is our last chance to do it with the four of us.||”|
Nasu is a slender girl with pale skin and delicate features. She has neck-length ash blonde hair styled in a bob cut with blunt bangs. Her eyes, turquoise with no pupils, change slightly in her trion body because she becomes more energetic. She often wears button-up jackets over light-colored shirts. Her uniform consists in a futuristic-looking white body-fit top with a square collar, purple gloves, an indigo belt that wraps partially around her waist, and a shoulder strap exposed on her right side. From the collar peers out the hem of a black shirt with a V-neck. The uniform sports six fake buttons arranged in two columns of three and a seventh right underneath the collar, on the right side; on the left is Border's emblem. The attire is completed by short black pants that connect into long purple boots.
Nasu is calm, well tempered and hardly gets carried away. Despite her frail appearance and constitution, she is strong-willed in battle and maintains a cool head under pressure. In the match against Tamakoma Second and Suzunari First she demonstrated an iron will which was not in small part motivated by her deep affection for her teammates and the resolve to climb as high as they could before Akane Hiura had to leave. The only time Nasu displayed any semblance of anger was when Wen Sō disguised herself as Yūko Kumagai.
Nasu and Kumagai share a strong friendship and care deeply for one another, so much so that Nasu was outraged by Wen Sō disguised herself as Kumagai and, right before defeating the Neighbor, she claimed that she was taking revenge for the injuries she had inflicted on her friend. In combat Kumagai often serves as Nasu's bodyguard. Nasu calls Kumagai by her nickname followed by the diminutive suffix -chan, while the latter calls her by her first name, without honorifics.
Nasu cares about her teammate and found more motivation to rank higher when she heard about Akane moving. Nasu addresses her by her first name followed by the suffix -chan whereas Hiura uses her surname and the honorific -senpai, reflecting their closeness as well as Hiura's respect for her captain.
As with her other teammates, Nasu appears to be friends with Shiki, whom she calls by a nickname followed by the suffix -chan; the Operator, on the other hand, addresses Nasu by her surname followed by the honorific -senpai as a sign of respect.
Rei is Narasaka's older cousin by three months, and she is the one who asked him to mentor Hiura.
- (To her teammates) "I don't know how many matches we'll have left. So... let's take the top! This is our last chance to do it with the four of us."
- (To her teammates) "I'll just have to defeat everyone on this side by myself."
- (To Osamu Mikumo) "Your actions... are still too unexperienced... Agent Mikumo."
- (To Yūma Kuga) "...What a shame... To have you rushing over here... It's a pity that I don't have trion left anymore. Damn it."
- (To her teammates) "I'm sorry... I didn't score four points."
- (To Wen Sō) "Every scar you left on Kuma... I'll return them back to you all at once."
- "Rei" (玲?) means "exquisite, clever, sound of jewels", while "Nasu" (那須?) is a traditional name for a region in northern Tochigi Prefecture.
- Nasu likes canned peaches, movies, her teammates, and exercising in her trion body.
- She has many secret admirers within Border.
- Her voice actress, Hōko Kuwashima, also voices Kyōko Sawamura.