Aya Drevis
"..Aya Drevis is a young girl, and the main protagonist of the game. She is the only child of Monika and Alfred Drevis, and lives in the large mansion that makes up the setting for the majority of the game..."
Older Aya
In the true ending, though, Aya's real personality was shown. It was implied that Aya might have turned out to be what her father was when she grew up; a sociopathic murderer. The red book her father had been reading was shown in her possession, having picked it up after leaving their burning home. Operating a small clinic in the middle of a forest, she shows goodwill to 'patients' to lure them unexpectedly to be experimented upon.
"I love you, father.."