Eri Amakazari, often called Ecchan by those close to her, is a second-year student at CITY South Middle School. She is a spirited and imaginative adolescent girl with short blue hair and blue or grey eyes, most frequently seen in her school uniform. During the summer, she also works at the Makabe family restaurant, having chosen to take a job there specifically to spend more time with her best friend.

At her core, Eri is a kind, supportive, and creative individual. While she shares an energetic and eccentric streak with her best friend, she often displays a surprising level of maturity and thoughtfulness. She can sometimes appear cool or even a little rude to her friend Matsuri, but this is typically part of the playful games they enjoy together or a way to mask her own deeper feelings to keep her friend from becoming sad. Her personality is described as being imaginatively eccentric in a very likable way, and she is warm-hearted and considerate. She possesses a free-spirited and creative imagination, often becoming the driving force behind her and Matsuri's adventures.

Eri and Matsuri Makabe are best friends and an inseparable duo, sharing a deep bond of trust and mutual enjoyment. They are members of the self-proclaimed "Going Home Club," though they rarely go straight home, instead inventing a series of whimsical and imaginary clubs to create their own adventures after school. In this friendship, Eri is often the one who initiates their stories and scenarios, with Matsuri acting as her supporter and coming up with extravagant titles for her, such as "Demon Lord Emperor". Beyond her friendship with Matsuri, Eri forms other meaningful connections. She is a regular customer of a barber named Kuratake, having earned his deep respect and a place among his top-ranked "short cut regulars" not by paying with goods, but with her kindness. When Kuratake lamented that his own grandchild never visits, Eri simply offered to be his grandchild, a gesture that moved him deeply. She also had a brief, one-sided affection for a boy named Takewaku, but after seeing him on a date with another girl, she and Matsuri concluded that their feelings were not truly romantic, and she decided it was more important to keep her friend company.

Her primary motivation is her friendship with Matsuri. Her actions, from taking a job to joining in on elaborate fantasies, are all driven by a desire to be with and support her friend. A significant development in her story is her planned move to the United Kingdom in the near future. This impending change adds a layer of poignancy to her daily life in the city, giving her and her friends a powerful reason to cherish their remaining time together. As a character, her role in the story is as the imaginative foil and devoted partner-in-crime to the more reactive Matsuri, with their independent storyline providing much of the manga's heart and humor. Her notable abilities lie not in physical prowess, but in her strong social intelligence, her capacity for kindness, and her boundless, infectious creativity that turns ordinary life into a series of fantastic adventures.