Chizuru Aizawa is a central figure in her community, serving as the manager and cook at the Lemon Beach House restaurant. As the eldest of the Aizawa siblings, she carries a significant burden, having taken on the role of primary caretaker for her younger sister Eiko and brother Takeru following the early loss of their parents. This background has shaped her into a person who prioritizes family stability and the success of the family business above all else.

Physically, Chizuru is notable for her tall stature, long indigo hair, and indigo eyes that she almost always keeps closed, giving her a perpetually serene and smiling expression. Her typical attire consists of the practical uniform of the beach house, favoring shorts over skirts or dresses, which suits her active role in the kitchen and around the restaurant. Her outward personality is the embodiment of calm, patience, and reserve. She often tolerates the chaotic antics of the curious sea creature Ika Musume with a gentle smile, treating many minor disruptions as harmless games.

However, this placid exterior conceals a truly formidable nature. Chizuru possesses abilities that far exceed normal human limits, reaching a level of near-flawless proficiency. She demonstrates exceptional strength, speed, and reflexes that are more than a match for Ika Musume’s superhuman tentacles, which she can snap with her bare hands. She also has other extraordinary skills, such as the ability to sense moving objects without using her sight and tearing clothing with a single touch. These talents are implied to come from a military background, though she reserves this power strictly for protecting her family, her employees, or the restaurant’s interests.

The trigger for Chizuru to shed her peaceful demeanor is any serious threat to her loved ones or the beach house. Comments about her weight are also a known point of sensitivity for her. In these moments, she opens her eyes, unleashing a terrifying and menacing aura that intimidates everyone around her, earning her descriptions such as "creepy," "terrifying," or even "not human". This fearsome presence is a key part of her dynamic with Ika Musume, whom she initially forced to work at the restaurant to pay for damages. While she can be friendly and tolerant, she is also a master of subtle manipulation, often testing the squid girl's abilities and keeping her invasion plans in check through sheer intimidation.

In her role within the story, Chizuru is the unwavering anchor of the Lemon Beach House, ensuring its prosperity and acting as the ultimate authority figure. Her key relationships are defined by this protective nature. With her siblings, she is a loving but firm parental figure. With Ika Musume, her dynamic is a complex blend of caretaker, tolerant boss, and secret sparring partner. The lifeguard Gorō Arashiyama harbors romantic feelings for her, but Chizuru shows no overt interest, seemingly prioritizing her familial duties above all else. She also has a hidden competitive side, which becomes evident when she swiftly and ruthlessly reclaims high scores on arcade games. Furthermore, she secretly operates under the alias of Noh Mask Rider Hannya, intervening incognito during events like beach stage shows or volleyball tournaments to restore order or aid her sister. While her core personality remains stable, her development is shown through her growing, albeit unconventional, tolerance for Ika Musume, subtly allowing the invader to become a part of the extended family she protects so fiercely.