From 闇(やみ) (yami, “darkness”) + 堕(お)ち (ochi, “連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 堕(お)ちる (ochiru).”).
やみおち • (yamiochi) ←やみおち (yamioti)?