Last Round Arthurs, Vol. 3 (Light Novel): The Snow Maiden and the King Who Killed Arthur, Paperback/Taro Hitsuji

You don't know what you have until it's gone. Luna is on the verge of death when a new King viciously attacks her using their Jack, Sir Tristan. Meanwhile, Rintarou joins forces with someone who used to be in the Dame du Lac, ready to go up against another version of himself. Neither Luna nor Rintarou are ready to give up their respective fights--especially if it means they have a chance to get back what's precious to them.