Mikoto Tachibana (橘 美琴,Tachibana Mikoto?) is Enkyou's daughter and Wataru's mother. She was good friends with Yukariko Sanzenin but according to Nagi, she went senseless after Yukariko passed away, thus relying on gambling for a living.
She has an extremely strong personality and makes a living off of gambling in Las Vegas. According to Nagi, Mikado Sanzenin was the one who taught her how to gamble. Furthermore, Nagi mentions that she is very strong like the devil.
She considers both Wataru and her husband to have very poor vision in what relates to business. When she is presented in the manga, it has been three years since the last time she and Wataru last met. She wanted him to live in America with her but then Wataru declined her offer which lead to a gamble match between her and Saki in order to determine where he would live.
The match started with poker, a game that Saki barely knew. During the heated match between them, Sakuya pointed out that Mikoto had an idea of the cards that Saki was playing with thanks to the refection of the cards in her glases and so they suggested to change the game to roulette, to which Mikoto agreed. All the odds pointed to her winning the match but a suggestion from Isumi, which conveniently showed up in the last minute, gave Wataru a clue about how to win.