Nagisa Aizawa (藍澤 渚 Aizawa Nagisa) is a classmate of Asahi and Yōko, and is also a small alien in a robotic exoskeleton. Initially the love interest of Asahi.
She, like most of Asahi's friends, is aware of his feelings for Yōuko, and develops feelings for him after the fact. Her species is militaristic, and she often uses military terminology when describing things. Her exoskeleton runs on an internal battery that must be recharged and has on many occasion run out for comedic effect. She is meticulous, though loses her composure when dealing with embarrassing situations. She has a brother whom she respects and draws inspiration from, though he is less reliable than she initially realizes.
She is younger sister of Aizawa Ryō.
Before the series began, she turned him down believing that her secret would be discovered if she started a relationship with him.