Kedarugena Koshaku Reisoku Ga Kawatta Riyu.

Kedarugena Koshaku Reisoku Ga Kawatta Riyu, known in English as The Reason Why the Sluggish Duke's Son Changed, is a light novel series authored by Mitsuki Beni. Emerging from the highly competitive web novel landscape in Japan, the series fits within the popular 'reincarnation' and 'villainous' tropes that define much of modern light novel output. It follows the narrative of a protagonist who finds themselves in a position of social and familial stagnation, tasked with navigating the rigid hierarchy of a dukedom while attempting to alter their own perceived character arc.

The character design and accompanying illustrations contribute to the series' distinct aesthetic, prioritizing a blend of refined aristocratic settings and the internal, often humorous, monologue of the title character. Mitsuki Beni utilizes this platform to explore themes of self-improvement and societal expectation, balancing the 'sluggish' nature of the protagonist with the political machinations typical of the nobility genre. The series has resonated with readers who appreciate character-driven stories where personal growth acts as the primary catalyst for changing the surrounding environment.