Motu Proprio (The King and the Neko) - Volume HaiYin
Lead characters are stepbrothers - Army General Gu Hai is the heir-presumptive pending The Crown Trials while his stepbrother Second Prince Bai Luoyin is a courtier; general is knowledgeable of the battlefield while courtier is adept at court; conflict is in that the general is very much in love with this stepbrother...