Sayori
☀️ The little bundle of sunshine ☀️
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Sayori is intended to play off the visual novel trope of the childhood friend who becomes a romantic interest. She is portrayed as being rather talkative, as she often goes on tangents. She cares deeply about the well-being and happiness of others, especially the player, and appears to be enthusiastic about everything. However, she makes it clear that this is a pretense due to her depression, and that it hurts her when people worry about her. Thus, she tries to keep everyone as happy as possible to make sure nobody needs to worry about her.
Her depression makes her very unmotivated to do anything, as she explains, which is why she's so often late to school, never cleans her room, and has short hair (to make it easier to take care of).

Monika
✨ The president of the Literature Club ✨
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Monika is an outwardly sweet character who cares about the well-being of her friends, but as the game progresses begins to favor the main character over the rest. She's a very philosophical individual, writing poems with deep allegorical content and discussing many topics beyond superficiality in Act 3. She is the only one of the four heroines not designed to fall into a character archetype commonly found in the visual novel genre, but many have interpreted her to be a yandere character, an archetype of someone who will do anything to be with their love interest, including murder.

Natsuki
Cute on the outside
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Natsuki is introduced to play off the trope of small-but-feisty tsundere girl, as discussed by Monika in Act 3. She's initially cold and not receptive to the main character but begins to be more open and emotional with him as time passes. Natsuki, uniquely, doesn’t seem to have any of her own problems and never meets a grisly end. However, hints are given throughout the story which suggest that her home life is troubled and that she struggles with a neglectful and potentially abusive family, including the ninth special poem and her edited comment in Act 2 about how her "dad would beat the shit out of [her]" were he to find her manga.

Yuri
❓ The Maiden of Mystery ❓
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Though usually very shy and overly apologetic, Yuri can be very talkative and enthusiastic when it comes to her favorite subjects, such as writing strategies and books she has read. For this reason, Yuri has trouble making and keeping friends, as she tends to come on too strongly. Yuri eats lunch alone at school, but claims she has company in the characters in her books. To that end, Monika warns the player that they may have trouble pursuing her, as Yuri probably has a fictional boyfriend. On weekends, Yuri prefers spending time with one or two friends, doing quiet activities at home, rather than going out.