The protagonist of the series. A 16-year-old high school student who became an orphan at a very early age and has been living in an orphanage since. Her dream is to become a daycare tutor. She's hired by Seiji after he witnesses how good she's with children, and becomes the Matsumura's official babysitter since, spending most of her time with them.
Eventually falls in love with Seiji, although decides not to confess since it'd get on the way of her work as a babysitter.
- All-Loving Hero
- Cool Big Sis: Acts as one since she's the oldest child in the orphanage.
- Expy: A young, cheerful orphan with long hair and good skills with children and housework? Has a mother complex? Sure you're not talking about Tohru Honda?
- Friend to All Children
- Oblivious to Love: Failed to realize Nao's feelings after all the years he crushed on her. Also, she didn't noticed Seiji reciprocated her feelings until he told her.
- Parental Abandonment: Her father died before she was born, and her mother when she was five.
- The Pollyanna: Ever positive, even with such a tragic past behind her.
- Single Woman Seeks Good Man: Ends up crushing on who's arguilably the most level-headed out of all the male cast: Seiji.
- Stepford Smiler: Never lets her weaknesses be seen. Except when she breaks down after her old house is torn down.
- Team Mom
- Tomboy and Girly Girl: The girly girl to Rio's tomboy.
The main male and the twins' guardian. A 25-year-old news presenter who recently became well-known due to his good looks. He's unable to balance both his busy work and taking care of the twins, so he hires Shiharu.
Falls in love with Shiharu and confesses to her, but since he's aware of their age difference, he tells her to wait for replying until she's older..
- Informed Attractiveness: Considered the most beautiful of all male characters.
- Megane: Wears them at home and when he goes out to avoid being recognized.
- Parental Neglect: His mother was a workaholic. His father usually spend the night with other women. They eventually got a divorce, and Seiji barely saw them at home.
- Sharp-Dressed Man: Part of his work attire.
- Tall, Dark, and Handsome: Gives off this vibe, although he's a very gentle man.
- Team Dad
- Workaholic: His lack of stamina after returning from work is what causes him to hire Shiharu.
Aoi and Akane Matsunaga
Two twins whose mother died in an accident and whose father ran away after the former's death. Until his return, they live with Seiji, and Shiharu helps him as their babysitter. Although at the beginning they look and act very similar, after they grow up they differ from each other: Akane becomes more upbeat and sociable, while Aoi is more level-headed (but still has a soft spot for sentai heroes)
- Always Identical Twins: When they're small. Later, Akane grows her hair out and starts using Hair Decorations, while Aoi has shorter hair.
- Big Eater: Akane.
- Half-Identical Twins
- Parental Abandonment: Her mother died when they were almost two years old. Her father ran away shortly after, and Seiji became their guardian, since no one else in their family could.
- Precocious Crush: Aoi has one on Shiharu.
- Token Mini-Moe
Shiharu's best friend: an energetic girl who always tries her best to support her in both work and love-related affairs. Develops a crush and later starts dating Takeshi.
Seiji's neighbour and childhood friend. An upbeat boy a few years older than Shiharu who attends his first year of university. Eventually starts dating Rio. He has two sisters: Mana, who's the same age as the twins, and Nanami, who attends middle school.
- Big Brother Bully: A bit when he was younger, with Nanami as her victim: he seems more responsible with Mana.
- Childhood Friends: With Seiji.
- Disappeared Dad: His father never appears (although his mother does have some significance to the plot)
- Oblivious to Love: He's terrible at reading the mood... which annoys the hell out of Rio, eventually kissing him to make him realize her love for him.
A boy in Shiharu's orphanage who acts mostly rude and cross. Attends a different high school, but he meets Shiharu back at the orphanage and they have a friendly relationship. He's had a crush on her for years, but after confessing and being rejected, eventually gives up.
- First Kiss: Took Shiharu's a long time ago while she was asleep, he's the only one who knows and decides to "take this secret to the tomb".
- Parental Neglect: His mother was an alcoholic and his father ran away, so he eventually was sent to the same orphanage Shiharu was.
- Patient Childhood Love Interest: Loved Shiharu since she met her, and has harvored the same feelings for 8 years. He's eventually rejected and decides to give up.
- Stalker with a Crush: Honoka, a girl from his school who's obsessed with him.