Chica Calamar, whose name in Japanese is Ika Musume, is the protagonist of her anime series. Her physical appearance is a direct reflection of her dual nature as both a sea creature and a humanoid girl. She has long, bright blue hair that is actually comprised of five prehensile tentacles, which she can move and control independently. She typically wears a white, dress-like outfit and a distinctive white hat that resembles the head of a squid, with a wide brim and two small side fins. Her large, earnest eyes and short stature contribute to her youthful and often innocent appearance, which contrasts sharply with her self-proclaimed mission as a fearsome invader.

Chica Calamar emerges from the depths of the ocean driven by a clear and serious motivation: revenge against humanity for the constant pollution and destruction of the marine environment. She arrives on the surface with the declared goal of conquering the human world as punishment for its contamination of her home. Her personality, however, is a blend of misplaced ambition and charming naivete. While she frequently declares her intent to invade and subjugate humanity, she is also incredibly clumsy, impulsive, and ignorant of even the most basic aspects of human life and customs. This disconnect between her grand mission and her daily reality is a defining trait. She can be easily distracted, is prone to childish outbursts, and often finds her plans of conquest derailed by her own mistakes or by simple, everyday activities.

Her central role in the story is established from her very first moments on land. Chica Calamar attempts to make the Lemon beach house, a small seaside restaurant run by the Aizawa siblings, her first base of operations for world domination. This initial invasion attempt fails spectacularly when she accidentally damages the restaurant's wall with her powerful tentacles. Unable to pay for the repairs, she is forced to work as a waitress at the Lemon, turning her from would-be conqueror into an indentured employee. This situation places her at the heart of the restaurant's daily operations, where most of the series' humor and character interactions unfold.

Throughout the series, Chica Calamar forms a complex web of relationships that shape her experience on the surface. Her relationship with the Aizawa sisters is foundational. Eiko Aizawa is the pragmatic and often short-tempered sister who takes charge of training Chica Calamar, frequently scolding her for her failures as a waitress and her grandiose invasion proclamations. In contrast, the older sister, Chizuru Aizawa, is calm and soft-spoken but possesses an intimidating aura that can instantly terrify Chica Calamar into submission when she misbehaves. The youngest sibling, Takeru Aizawa, is a young boy who looks up to Chica Calamar as an older sister figure. Unlike the others, he enthusiastically plays along with her invasion fantasies, seeing her as a friend and playmate rather than a threat.

Her interactions with other humans further showcase her growth and the contradictions in her personality. She develops a friendship with the lifeguard Gorou, whom she respects as a fellow defender of the sea. She also becomes the object of obsessive affection for Sanae, a friend of Eiko whose fixation on Chica Calamar often borders on frightening. Chica Calamar's initial stance of pure antagonism toward humanity gradually softens through these connections. While she never fully abandons her goal of invasion, she develops genuine affection for many of the people she meets and begins to find enjoyment in her life on land, even as she continues to complain about the work she has to do.

As the narrative progresses, Chica Calamar shows subtle but important development. She learns to navigate the customs of the human world, albeit imperfectly, and forms strong emotional bonds that complicate her original black-and-white view of humans as mere polluters to be conquered. Her understanding of concepts like friendship, celebration, and responsibility grows, even if her pride often prevents her from admitting it. This development is not a dramatic transformation but a gradual softening of her character, making her more integrated into the community she once swore to overthrow.

Chica Calamar possesses a unique set of abilities derived from her squid physiology. Her most prominent feature is her ten tentacle-hairs, which are incredibly versatile. She can use them to lift heavy objects, deliver powerful strikes, perform delicate tasks like cooking or drawing, and even move herself with great speed. Another common ability is the expulsion of a thick cloud of black ink from her mouth, which she can use to blind pursuers or escape from trouble. She can also make her body glow with bioluminescence, and she wears special bracelets on her wrists that allow her to regulate her weight, enabling her to float or become incredibly heavy at will. For all her power, she also has significant weaknesses. She has a paralyzing fear of orcas and sharks, who are natural predators of squids. She is also highly vulnerable to fire and heat. Furthermore, she firmly believes that if her iconic squid-shaped hat were ever removed, she would die. These vulnerabilities often prove to be a greater obstacle to her conquest than any human defense.