Kana is a playable character in Fire Emblem Fates. Either he or she is the child of the Avatar as well as the grandchild of Mikoto. Kana's in-game gender is the opposite of the Avatar's gender.
Kana is the child of the Avatar and the grandchild of Mikoto. If the male Avatar is married to Azura, Kana becomes Shigure's sister. Any other mother will leave female Kana an only child. Male Kana can be the brother of all possible children in the game except for Shigure.
Shortly after being born, Kana was placed in the Deeprealms for their safety so they could be raised free from the war between Hoshido and Nohr. From time to time, the Avatar and their spouse would come over and visit to make sure that Kana was okay. After several years in the Deeprealms, Kana grew excited when they learned that the Avatar was going to pay them a visit.