|“||...What a shame... To have you rushing over here... It's a pity that I don't have Trion left anymore. Damn it.||”|
Nasu has neck-length ash blonde hair styled in a bob cut with blunt bangs. She also has blue eyes with no pupils.
In Trigger Mode, she, along with her teammates, wears a white body-fit armor over the top half of her body with purple gloves, a belt that wraps partially around her waist, and a shoulder strap exposed on her right side. This is connected to short black pants that then connect into long purple boots.
Nasu is a rather quiet and sickly girl, as she is often shown sitting in bed. She's calm, well tempered and hardly gets carried away. However, despite her frail appearance, she is strong-willed when in battle and maintains a rather calm front even when under pressure, as she was able to garner 3 points for her team even though the odds were stacked against her. She also highly values her teammates, seeing as they were her primary driving force during the rank battles, and how violent she became after Wen Sō disguised herself as Kumagai to trick herself.
She cares about her teammate and found more motivation to rank higher when she heard about Akane moving.
- (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 4 points." 
- "Rei" (玲?) means "exquisite, clever, sound of jewels", while "Nasu" (那須?) is a traditional name for a region in northern Tochigi Prefecture.
- Her voice actress, Hōko Kuwashima, also voices Kyōko Sawamura.
- She likes canned peaches, movies, her teammates, and exercising in her Trion Body.
- She has many secret admirers within Border.
- Rei is Narasaka's older cousin by 3 months, and she is the one who asked him to mentor Hiura.
- Her eyes change slightly in her trion body because she becomes more energetic.[BBF Q99]