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 with the collar slightly unbuttoned topped off with a red ribbon, although unlike the others, Sayori also keeps her blazer unbuttoned. She also wears a dark blue skirt, white knee-high socks and white uwabaki slippers with sky blue tips. The protagonist points out to Sayori the next 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 initially 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. However it is later revealed that she suffers from bad depression and works so hard to make the people around her happy to cope with her own lack of self-love amongst other things. She is also usually the only character, other than the protagonist, shown to break up arguments, Monika noting that her sentiments are necessary to keep 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 is also introduced as the main character's best friend. The main character seems to view her as airheaded and slightly annoying at the beginning of the game, however, he starts to sympathize with her after Sayori confesses about her depression.
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's depression seems to make her struggle with the conflict of that she doesn't think she deserves to be loved but at the same time deep inside her heart, like anyone desperately wants to be loved, especially by the main character. This is why when the player chooses to pursue one of the other girls Sayori's seems to suffer because she secretly wants the player to love her while at the same time experiencing guilt for feeling bad in the first place (of course is her illness also gradually amplified by Monika at this point). However, if the player actively chooses to pursue Sayori's route she will experience guilt anyway since she doesn't believe that she deserves to be loved and will thus, either way kill herself, no matter what the player chooses. 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. Sayori also shows to have a fondness for food, as shown in one of her poems, and after eating Natsuki's cookie without her permission.
When Sayori confesses her love for the protagonist, she will either hug him or run away with a pained expression (depending on the player's choice.) The next day, the main character will go to school without her, assuming she was still asleep. There, he will read a poem written by Sayori named "%", with the words "Get out of my head" repeated constantly. This will cause the protagonist to panic and go to Sayori's house, where she will be found dead, hanging from a noose with blood on her hands. If the player tries to load their save after her suicide, the game states that the save files are corrupt and completely reboots, as if Sayori never existed. This would mark the end of Act 1.
After Monika restores each member's file, at the start of Act 4, Sayori will again be present on the game. Natsuki and Yuri will also be present. This time, Sayori is the club president instead of Monika. Towards the end of the game, one out of two endings will happen. If the player achieves the normal ending, Sayori will reveal that since she is now also self-aware, possibly because she is now the club president, and will thank the player for deleting Monika. The scene then moves from the club into the room Monika was in during Act 3, as she claims how happy she will be to be with the player forever. Monika will then delete Sayori, stating that she "won't let her hurt him," and then will delete the entire game.
If the good ending is achieved, Sayori will instead thank the player for spending their time with all of the girls, saying that it's all that she wanted all along. Sayori will then thank the player for playing Doki Doki Literature Club and with a few tears in her eyes say that they all love the player.
- 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's file can be decoded into an .ogg file, which will play some sort of high screeching. Running the audio through a spectograph will reveal a QR code, which leads to the Project Libitina website.
- 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 has no traditional meaning. Interestingly, although Dan doubted it to even be a real name, it is one, although very uncommon.
- As also noted in the fan pack booklet, Dan chose Sayori as the character who inadvertently sets off the horror side of the game largely because he knew it would hit anime fans the hardest, ie. seeing the archetypal girl who wants everyone to be happy be the one to commit suicide.
- In a livestream celebrating the first anniversary of the game's release, Dan cited the character Yui Hirasawa from K-On! as an inspiration for Sayori's character.