The 4:44 ceremony, according to urban legend, involves utilizing a radio player to emit frequencies in front of the Akeyuki Sacred Tree at exactly 4:44, sending people to another dimension. When Asuka Tsuchimiya and her Crystal Radio Research Club companions Nana Nanase, Mia Silverstone, Yuu Tounaka, and Chloe Morisu decide to execute this ritual as a club activity, they are surprised when it works. The five journey to a fragment, a parallel universe where they encounter an unsettlingly familiar girl—parallel-world Asuka's self. Seriouska is the name given to this Asuka because of her serious demeanor and fighting prowess.