A surf-loving girl who starts working at the Lemon Beach House. She has an older sister, Aiko Saitou.

Unlike everyone else, she sees Ika as an actual threat to humanity, and is genuinely afraid of her. She often tries to warn the others and get them on the same page, though, nobody else feels the same way. Ika enjoys the fact that Nagisa fears her and constantly teases her whenever she can. Nagisa is also a high-schooler, but does not attend the same high school as that of Eiko Aizawa and Sanae Nagatsuki. In addition to being a keen surfer, Nagisa also rides a bike and can jump rope. Nagisa also likes watching magical girl and tokusatsu shows on TV in her spare time.