Shio Kōbe is a young, innocent girl who lives with Satō Matsuzaka in their apartment. She loves and cares for Satou deeply, but often remains blissfully unaware of Satou's endeavors aside from Satou's necessary attendance in school and work, as she is not allowed outside of the apartment.
Shio has blue eyes and black hair tied into two pigtails. She usually wears a sailor-style school uniform which includes a light blue long-sleeve shirt, a striped blue bow tie, and a blue plaid skirt. Since Shio rarely ever goes outside, she is never seen wearing shoes but wears black under-the-knee socks.
Shio is a kind and innocent girl who tries her best to work hard and watch over the house while Satou is away at school and work. She routinely greets Satou whenever she returns home and is always genuinely happy to spend time together with Satou. Shio believes that both she and Satou need to stay together, otherwise they would both be broken and incomplete forever.
While her interactions with other people besides Satou are limited, she still displays the same kindness and sincerity she would with Satou, which draws many people to her. She is typically referred to as an "angel", a "light", "the Moon", and other otherworldly symbols and beings, suggesting that her purity is a rare and enlightening trait of her personality that makes her almost ephemeral.
When Shio was born, her mother felt sorry for her because she was born into a cruel world with her abusive father. Asahi, however, suggested to his mother that they should work hard to protect her, and Shio soon became a ray of hope for the two of them. At some point, Asahi urged his mother to run away with Shio and he would stay behind so that their father wouldn't try to find them. He promised to return to his mother and Shio, and made a vow.
Eventually, Shio's mother found a place for them to settle in, waiting until the day Asahi returned, but struggled to keep up with paying rent because of her inability to get a well-paying job. Shio noticed that her mother was slowly breaking apart and tried her best to cheer her up, however Shio's attempts at comforting her mother were often futile, as her mother fluctuated between many emotional extremes due to her past and current circumstances. Because of her mother's fear that her father would find them again, Shio's mother forbade Shio from leaving the house and got angry whenever Shio disobeyed her, despite Shio's intentions to help her mother feel better (such as going outside to pick a flower for her).
As her mother's state was gradually diminishing waiting for Asahi to return so that they could be happy, Shio begged her mother to take her outside so that she could find something to help fix her, but almost got in a car accident because of it. Shio was immediately brought back home and was scolded for wanting to go outside even though she only wished to help. For the first time in her life, Shio's mother slapped her, but quickly broke down due to the resemblance between her actions and her husband's abuse.
Soon after that incident, Shio's mother decided to take Shio outside again during a rainy night, and pushed Shio into an alleyway. Despite Shio begging for forgiveness and promising to be obedient, her mother stated that she no longer needed her, and left Shio by herself. It was at that moment that Shio encountered Satou, and noticed that her "jar was empty, but not broken" because she still believed in something, unlike her mother's "jar", which Shio believed was broken due to her selfishness. This caused Shio to wish to forget everything that happened, and because of this, Satou chose to take her in.
Presently, Shio lives with Satou in their apartment and is often left alone for most of the day because of Satou's school and work obligations. She is perfectly capable of leaving the apartment (before Satou installs a lock from the outside), but does not do so out of her own will due to Satou telling her about the dangers of the outside world. She is blissfully unaware of the fact that Asahi is searching for her.
- Shio (しお) means "Salt" in Japanese.
- Shio seemingly has the ability to "see" people's hearts as jars, noticing that her mother's jar is "empty and broken" and Satou's jar is "empty, but not broken".
- In attempts to remember her mother and Asahi, Shio suffers symptoms ranging from dizzy spells, intense fear and anxiety that leave her curled up on the ground with a headache, and even hallucinations of her mother with her face scribbled out, speaking to her. Though there is no name for her condition, it may have originated from her past desire to forget everything that happened with her mother.
- Shio is (probably) 5-9 Years Old.