After the Substitute Marriage, I Joined Forces with the Sickly Prince

The surface story: An unpopular concubine is forced to marry the seventh prince, who is rumored to be sick and dying, for her eldest sister, but is accidentally involved in a turbulent battle for the eldest son. The inner truth: The concubine is actually a clumsy chess player, and the prince is also a forbearing organizer. The two saw through each other's disguise in a desperate situation, from a mutually beneficial alliance to a sincere commitment, and finally joined forces to eliminate