Monika Drevis - also referred to as simply "Aya's Mother" in the Japanese version - is the late wife of Alfred Drevis and Aya Drevis's mother She serves as the game's main antagonist. She passed away about a year ago before the events of the game and has come back as a vengeful spirit.

Monika is initially portrayed as a kind and forgiving woman who tends to overlook the mistakes of others, often trying to see the good in everyone. Following her death, she became a vengeful spirit hellbent on getting her revenge, even reviving the victims of her husband to do so.

In truth though, Monika is not as innocent as she appears. She can be quite manipulative and can easily read people's hearts. During her youth, she often sends letters to various killers, asking them to tell her about the various murders they committed. She was also quite fascinated by her grandpa's research into turning people into dolls, and couldn't understand why her aunt was against it, as she thought that what her family was doing would allow people to leave more of a mark on the world.

In spite of this, her love for her family seems to be genuine. Monika's diary reveals that she adored her grandparents and didn't want to disappoint either of them despite both of them wishing different things for her. While Monika was alive, she frequently doted on her daughter Aya. She even tried to prevent Aya from learning the truth of her death, only relenting when her daughter chose to save Alfred instead of letting her take her husband away with her to the afterlife. On the flipside, Monika had no problem trying to groom Aya into becoming a cruel individual so that she could carry on the legacy of Monika's grandfathers, though Monika did allow her to grow up rather freely.

Monika is also quite in love with her husband Alfred and was deeply hurt when she discovered he was cheating on her with the family maid, Maria, though she never confronted the two about it. However, once she learned that Alfred planned on turning Aya into a doll in order to preserve her innocence, she threatened to leave with Aya in tow, which resulted in Alfred killing her. In spite of that, she admits to Aya that she still loves Alfred and couldn't bring herself to kill him.

Monika also appears to have been a good cook, occasionally cooking Aya's favorite: hamburger steak (in the original/2.02 version) or sirloin steak (in the 2020 remake.) Monika is also implied to have an interest in charms. A book Aya can find called the "Charm Encyclopedia" talks about casting good luck on someone by kissing them on the forehead and saying a blessing, which she is shown doing to both Aya and Robin in certain parts of the game's story. Said book also has another chapter (only seen in Blood Mode) about birthing a boy, which implies that Monika hoped to have a son instead.