Takeru Aizawa, the younger brother of Eiko and Chizuru, lives with his sisters at the Lemon Beach House restaurant. This third-grade elementary student sports black spiky hair and gray eyes, often dressed in a green t-shirt and brown shorts, making him the only family member not in long pants and reflecting his energetic nature.

Cheerful, friendly, and openly curious, Takeru frequents the quieter beach near the restaurant. He holds a particular fascination for Squid Girl's tentacles, finding them amusing and entertaining. Despite her initial disinterest and irritation, especially when his perception of her as "cute" undermines her attempts to be intimidating, Takeru persistently seeks her companionship as a fascinating creature and potential playmate. He remains undeterred even when she reacts by physically swinging him around or trying to discipline him.

Squid Girl's attitude gradually softens from annoyance to genuine friendship. Takeru now plays regularly with her and his school friends, Yuta Matsumoto, Shota Kuroishi, and Satoshi. They share the same elementary school class, taught by Aiko Saito. Takeru actively involves Squid Girl in games and activities at home, integrating her into his social circle and playing a key role in acclimating her to human interactions and surface-world experiences.