Every night, Hanako Tanaka closes her eyes and becomes someone else.

She didn't have good experiences in the real world. Job as a data analyst isn't what she dreamed of, so she escaped into the world of her dreams. Arithmia is a world she has crafted for years, and whenever possible she enters it through her lucid dreams. As her dreamself, "Lucy Dorima", she gets to live a life she wanted, even if it's all in her head. But is her shelter truly as safe as she hoped for?