Mea

Japanese name:

メア

Mea, the three sister's maid, is actually a life-like android. She later rejoins the group, along with Mai, when the mansion returns 5 years later to the same spot.
Later it's revealed Mea is a guide for the girls set to help them along their journey. Further on it's shown Mea is working with Shizuku along with Keith.

MAL