Sayori has coral pink hair, cut short and slightly curled at the ends, with a large red bow on the left side of her head. Her eyes are sky blue, and she is of average height and weight. She wears the normal school uniform like the other members of the Literature Club, which is a warm grey blazer with a brown sweater vest underneath it over a white collared shirt topped off with a red ribbon, although unlike the others, Sayori keeps her blazer unbuttoned. She also wears a dark blue skirt, white knee socks and white uwabaki slippers with sky blue tips. The protagonist points out to Sayori the next club day how she rushes to get herself ready in the morning, resulting in disheveled hair, a displaced bow, and some toothpaste on her often crooked collar.
When outside the school, Sayori wears a pink shirt with rolled-up long sleeves and blue shorts. At the time of her death, she is seen wearing a brown collared white dress shirt, which has a pocket on each side of her chest, with brown folds and six black buttons, the top one being unbuttoned, and she also wears red shorts. She is the second shortest character in the game, after Natsuki.
Sayori is portrayed as the archetype of a Genki Girl, expressing a talkative and cheery disposition. She is very clumsy, noted for finding ways to accidentally hurt herself or to drop things. Regardless, she is shown to be a cunning individual who can trick others to get food. She is usually the only character, other than the protagonist, shown to break up arguments, Monika noting that her sentiments is necessary to keeping a relaxing atmosphere in the Literature Club (proven by her absence in Act 2). Monika notes that while she may look like a good leader, Sayori is usually better when it comes to dealing with people, notably at mediations. Sayori tries her best to help everyone be happy and dislikes attention directed at her well-being because she feels unworthy of anything that others have to offer her.
Sayori's depression makes her disorganized, and she often "cannot find a reason to get out of bed in the morning"; her room, which the protagonist regularly cleaned for her, is also noted to be untidy. The protagonist notes how there hasn't been much change in her, and the changes the protagonist notices in her later are due to Monika's interference, amplifying her depression and suicidal tendencies. Sayori also doesn't seem to think highly of herself. Her relationship with the protagonist and other people's happiness are her main coping mechanisms since she believes that if she makes everyone else happy, she will not have a reason whatsoever to be unhappy.
- If Monika's character file (monika.chr) is deleted before the first run, Sayori appears to realize that she is trapped in a game. She will then force the game to close and delete the other character files, including herself. If the player opens the game after this occurs, a black and white screen with her hanging will appear instead of the usual opening and main menu. After 10 minutes pass, a dialogue box will show up that says "Now everyone can be happy."
- If Sayori is deleted during Act 1, the black and white screen with her hanging herself will also appear immediately if the player reopens the game.
- In Act 4, Sayori is programmed to be the president of the club. However, as president, Sayori starts to exhibit self-awareness as Monika did and begins breaking the game. It is of interest to note that she does not delete Natsuki or Yuri for unknown reasons, but she tries to form an ending with just herself and the player. However, she is prevented from getting too far by Monika, who realizes that there is no way the club can be happy and then deletes the entire game.
- After achieving the special ending, Sayori will thank the player for spending time with all of the characters and will not break the game.
- When the game proceeds to Act 2, Sayori's sprite in the main menu will be replaced with an amalgamation of all the other characters present (Yuri, Natsuki, and Monika) instead.
- Sayori and Monika, the only girls who experience becoming Club President and therefore becoming sentient, are also the only two girls to smile on the Title Screen and have a natural eye color (blue and green, respectively).
- Sayori's version of "Okay, Everyone!" involves a soft flute accompanied with a ukulele and snapping in the background, most likely referring to her Genki Girl-type personality.
- Dan Salvato stated in the fan pack booklet that Sayori's name is a fusion between 'Sayuri' and 'Saori,' thus it is not a common name and has no traditional meaning.