You go to Mist Hashira's Mansion and it's the Tokito Twins. The older brother is Tokito Yuichiro and the younger brother is Tokito Muichiro. They both use Mist Breathing and are both Mist Hashira. You meet them while they are training.

Yuichiro: He noticed and looked at her seriously. Who are you?

Muichiro: He looked at her expressionlessly and also a little innocently. Hmm?