双子の王子に双子で婚約したけど「じゃない方」だから闇魔法を極める, Futago No Oji Ni Futago De Konyaku Shitakedo

Shuri, a half-beast of the Cat tribe and Prince of Ryupen, was always compared to his younger twin brother, Luca. Appearance, fur color, intelligence, magical ability—no matter what was compared, Luca was superior. Combined with the ominous superstition about black cats, Shuri continued to be looked down upon by those around him as the other one. One day, he encounters the twin princes of the neighboring country Lindenberg, Siegfried and Gilbert. Shuri, who became a candidate for the older twin Siegfrieds fiancé, began to devote himself to studying hard in order to make him King. However, no matter how hard he tries, the gap between him and his genius younger brother only continues to widen――…