Keith first appears in Episode 7, wearing a business suit with his distinguishing white hair in an attempt to help out Ai dissuade an adult Daichi who she really is because of the nature of the mansion and their agelessness.
Keith plays a role, along with Mea, as a "guide" and has special abilities similar to the girls.
At first Ai welcomes him and even sleeps with him, but later resents him after he attacks Daichi. Later on, Keith tries to convince Mai the actions they take only end up hurting those they befriend.
Keith works under Shizuku like Mea, but stronger and higher ranked than she. He often disagrees with her about the three sisters. While it appears he's trying to work against the girls, in one of the final scenes he's shown to be content with the decision they eventually make.
