Not every girl receives what she wishes for on her sixteenth birthday, but Kobeni's present is something she never anticipated: a prearranged marriage! Because of her deceased grandfather, Kobeni has been betrothed to a complete stranger since childhood, and although she allegedly met him, she recalls nothing about him. Even stranger is that her mother and her overly affectionate sister, Benio, appear entirely unfazed when the intended groom, Hakuya, and his younger sister, Mashiro, arrive at their doorstep to live with them. However, it is only after they begin attending Kobeni's school that events become even more peculiar, as she starts noticing some very... unusual vibes from her prospective future family. From Mashiro's fixation on extraterrestrials and UMAs (Unidentified Mysterious Animals) to Hakuya's disturbing absence of emotion, there is something quite odd about them that Kobeni cannot quite identify. What has her grandfather involved her in, and how does this connect to the unexplained blank in Kobeni's memory?