Futakoi Alternative follows Rentarō Futaba and his detective agency. One day, a pair of twins, Sara and Sōju, appear at his door. They move in with him and serve as secretaries for his agency. It is extremely difficult to classify Futakoi Alternative into a specific genre, though at its core, it is most similar to a romantic comedy. The first few episodes are lighthearted, but the series grows more serious as it nears its conclusion. The criticisms of the show are typically the same as its praises: namely, that it never fully settles into any single genre or style, switching between them from episode to episode (being almost equal parts romance, action, sci-fi/fantasy, and comedy).