Previous Next "Yuudachi Houteishiki" (夕立方程式, lit., "Evening Shower Equation") is the opening theme song of the Sodachi Lost story arc in the Owarimonogatari anime series. The song was not used in the TV broadcast of the anime series, and was instead first released during the single release of the song. It is performed by Marina Inoue, who voiced Sodachi Oikura.