Gorou Arashiyama is a supporting character recognized for his role as the local lifeguard at the beach where much of the story takes place. He is physically characterized by his tall, athletic, and well-muscled build, which is typically on display as he is often seen shirtless, wearing only a pair of swim trunks. His appearance is further defined by his tanned skin, short brown hair that reaches his ears, and brown eyes, marking him as a distinctly outdoorsy and active teenager.

True to his profession as a lifeguard, Gorou takes his duty to protect beachgoers seriously. Despite his strong and capable exterior, he possesses a notably gentle and somewhat shy personality, especially when it comes to matters of the heart. His primary motivation and most defining personal characteristic is his deep, unspoken romantic feelings for Chizuru Aizawa. He is perpetually in love with her but lacks the courage to confess his feelings, a predicament that forms the core of his character arc. He is regularly seen trying to work up the nerve to approach her or express his affection, only to become flustered or tongue-tied, which provides much of his character-driven humor.

In the context of the story, Gorou is a regular visitor to the Lemon beach house, which serves as the main setting and is where Chizuru works alongside her sister Eiko. His interactions with Squid Girl are unique because of his affinity for the ocean. Squid Girl initially has a critical view of him, believing that a lifeguard who only protects humans from the sea does not truly act as a "protector of the sea" itself. Over time, however, their relationship develops, and he comes to respect her unique connection to the ocean, understanding that she protects the sea in her own way. He also serves as a foil to Squid Girl's often naive and invasive schemes, reacting with a grounded, albeit easily flustered, sensibility.

Beyond his crush on Chizuru, his key relationships include a professional and friendly rapport with other staff and regulars at the beach house. He is kind and patient with Eiko and Takeru, the younger Aizawa siblings, and has a tolerant understanding of Squid Girl's eccentricities. As a lifeguard, his notable abilities are centered on physical strength, endurance, and exceptional swimming skills, all of which are necessary for ocean rescues. While he does not possess any supernatural powers, his competence and bravery in the water are well-established, making him a reliable figure whenever a crisis occurs at the beach. His journey throughout the series sees little change in his romantic situation, but he grows more comfortable in his role as a friend and ally to the growing cast of characters, learning to better communicate and trust those around him.