Yui Hotori was once a close friend to Souko Hoshina and Alto Tsukiyomi. As such, both the family Hotori and the family Tsukiyomi were close. He was forced by Souko to end the friendship when Aruto went missing. He was the one who gave the Dumpty Key to Tadase, although the reason for him to be holding it in the first place is still unknown.
Yui looks like an older Tadase but his hair color grayish brown.