Originally, DARK and KRAD had been sealed, but a girl, Hoshino Yukina, unsealed them by mistake and took them home to live. Hoshino Yukina is a lonely girl, 14 years old, studying at Higashino Middle School. Due to work, her parents are not at home all year round, so since she was five years old, Xuena has always been eating and sleeping alone, feeling extremely lonely. But since DARK and KRAD came, she gradually became cheerful and lived happily every day...