Melon is a steel Akikan, a being that transforms from an empty beverage can into a human-like form. She originates from a can of melon soda purchased by a high school student named Kakeru Daichi, and he gives her the name Melon. She is a central figure in the story as his partner.

In appearance, Melon has long blonde hair and distinctive green eyes that reflect her melon soda origins. A large, green, melon-shaped headdress is attached to the right side of her head, which can sometimes react to her emotional state. Her usual outfit, both in daily life and in battle, is a green sleeveless dress featuring a melon-like plaid pattern. Through Kakeru's efforts, she is able to transfer into his high school class, where she pretends to be his cousin who has come to study from Denmark.

Melon has a personality that is often described as competitive and strong-willed, which leads to frequent arguments and comedic fights with Kakeru. She is a classic tsundere archetype; while she develops genuine romantic feelings for him, she struggles to express them openly. She often acts cold or says the opposite of what she truly means, hiding a lonely and more vulnerable side beneath her tough exterior. This behavior is sometimes compounded by jealousy when Kakeru interacts with other female characters or drinks other beverages.

Her primary motivations evolve throughout the story. Initially, she participates in the Akikan Elect project, a government-sponsored conflict to determine the superiority of steel cans over aluminum cans. However, her deeper, personal motivation becomes her desire to protect Kakeru and build a meaningful bond with him, as she feels lost without her owner. Her role in the story is that of a magical girlfriend and combat partner to Kakeru, but she is also a key player in the battles against other Akikans. She harbors a distinct dislike for aluminum Akikans, leading to frequent quarrels with Yell, who is an aluminum sports drink Akikan.

Melon has several key relationships that define her role. Her dynamic with her owner, Kakeru, is the most important. It is a turbulent relationship of bickering that slowly develops into mutual affection and loyalty. A key moment that deepens her protective instincts is learning about a traumatic incident from Kakeru's past, in which he had to protect his childhood friend. Her relationship with other Akikans, especially her rivalry with Yell, is initially hostile but develops into a more complex partnership over time.

In terms of character development, Melon begins as a combative and emotionally closed-off being but gradually opens up to Kakeru and others, becoming more expressive of her loneliness and her need for connection. The central themes of her story often explore loneliness and the desire for a place to belong. While she remains a tsundere character throughout, her experiences help her become more loyal and emotionally reliant on her friends.

As an Akikan, Melon possesses notable abilities based on carbon dioxide, which is referred to as cool drink sorcery. Her powers include generating a carbonation attack that she calls Melon Melon Melon, a green magic ball resembling a melon. She can also use defensive techniques like the Yubari Barrier, a green magic shield named after a region famous for melon production. Another ability is Decameron, which involves restraining an opponent using her green magic. Her overall combat ability is considered to be very high among other Akikans. Outside of battle, she develops a quirky hobby of watching baseball on television, becoming a fan of the Hanshin Tigers baseball team despite admitting she does not fully understand the rules of the game. To earn money and experience the world, she also works part-time at a maid cafe.