Futago no Ouji ni Futago de Konyaku shita kedo "Ja Nai Hou" dakara Yami Mahou wo Kiwameru

Shuri, a half-beast cat prince from the kingdom of Leupen, has spent his whole life living in the shadow of his gifted twin brother, Luca. Superior in looks, fur color, intellect, and magical talent, Luca is adored by everyone, while Shuri is despised and dismissed as "the other one"—a stigma worsened by local superstitions regarding black cats.Things take a turn when both twins are arranged to marry Siegfried and Gilbert, the twin princes of the neighboring powerhouse Lindenberg. Upon learning that Lindenberg's royal succession will be decided based on which brother has the more capable mate, Shuri falls deeply for his fiancé Siegfried and dedicates himself to studying relentlessly to help him win the throne. However, unable to bridge the gap with his genius brother, Shuri resolves to specialize in the one discipline where he can carve out his own identity: dark magic.