Yui

Mt. Iwaki Yukisato Shirona's 55th Child (岩木山雪里白那の五十六子結,, Iwakiyama Yukisato Shirona no Gojūroku-shi Yui) or simply Yui (結, Yui), is Akira's older twin brother. He was the former chief of the Snow Village and the former user of the nil calculus.