Mare

The sisters' maid.
She appears to behave like if she had no emotions at all, especially at the beginning of the game, but Mare later proves that she does have her own desires. She also becomes friendlier with Chris as the story progresses to various degrees, depending upon whether it's her scenario or not.
Is disliked by Mai who calls Mare "Roboko" rather than by her name, always threatened to be destroyed or to be disposed of by her

Spoiler

though Mai comes to accept Mare in the end of her route, even calling her by her name

.

Spoiler

She is actually a human who was disabled to the point that she was unable to do anything due to her brain being unable to cope with the Popotan-phenomenon.
She was picked up by Claude who brainwashed her into believing she's an Android, naming her Mare. She is then sent to the house of the three sisters to investigate the cause of their psychic powers under the cover of working as a maid.