Kokoro (Kokoro Anzai) / Age: 7th Grade (12–13 years old). Era: 2006. Traits/Role in the Castle: The protagonist. She became a shut-in and stopped attending school due to relentless bullying from classmates. While reserved at the castle, she is a kind girl who empathizes deeply with the pain of others.

Rion (Rion Mizumori) / Age: 7th Grade (12–13 years old). Era: 2006 (Same as Kokoro). Traits/Role in the Castle: A handsome boy with refined features. He was sent to study at a school in Hawaii by his mother's wishes; though enrolled at Yukishina Fifth Junior High, he cannot attend. He is skilled at soccer and serves as a friendly, kind mood-maker who treats everyone frankly.

Fuka (Fuka Hasegawa) / Age: 8th Grade (13–14 years old). Era: 1979. Traits/Role in the Castle: A gentle, serious girl who wears glasses. Her piano talent blossomed in early childhood, and she was expected to be a "prodigy" by those around her, but the pressure and grueling practice schedule have worn down her spirit.

Subaru (Subaru Nagahisa) / Age: 9th Grade (14–15 years old). Era: 1966 (The oldest era among the members). Traits/Role in the Castle: A tall boy with a somewhat aloof air. Though he appears cool at first glance, he is very calm and mature. He struggles with the collapse of his complex family environment, including his parents' divorce and remarriage, and his relationship with his brother.

Ureshino (Haruka Ureshino) / Age: 7th Grade (12–13 years old). Era: 2032 (The furthest future era among the members). Traits/Role in the Castle: A chubby boy who loves to eat. He is a flirtatious jokester who quickly falls for girls and makes moves that usually backfire. However, he is the one who triggers a shift in the castle's atmosphere by being the first to reveal his reason for not attending school.

Aki (Akiko Inoue) / Age: 9th Grade (14–15 years old). Era: 1992. Traits/Role in the Castle: A reliable, big-sisterly girl who looks good in a ponytail. She is a dependable figure who leads the castle members, but in her private life, she suffers from isolation in her overly strict volleyball club and a painful, complex home environment.

Masamune (Sei Masamune) / Age: 8th Grade (13–14 years old). Era: 2019. Traits/Role in the Castle: A boy who loves video games and speaks with a slightly cheeky tone. He is logical and proud, sometimes lying to save face, but he is fundamentally caring toward his friends. He stopped attending school because he couldn't fit in with those around him.

Wolf Queen. True Identity: Mio Mizumori. Appearance in the Castle: A small girl wearing a wolf mask and a red frilled dress. Role: The "guide" and host of the castle inside the mirror. Personality: Appears arrogant and overbearing at first, speaking with a cheeky tone. However, at her core, she possesses a deep kindness and concern for the children.