Natsuki has straight pastel pink hair, cut around chin length, and pink eyes. Her bangs are swept to the right, having two prominent strands of hair beside them. Her accessories consist of a red Japanese-style crossed hairclip, as well as two red ribbons tying two small ponytails on either side of her head- the rest of her hair left down. Her canine teeth are longer than the rest of her teeth, making them visible when she opens her mouth wide enough. She is the shortest character in the Literature Club, a feature that results in people commonly mistaking her for a first-year student.
Natsuki wears the traditional school uniform just like the other characters for the majority of the game, which is a warm gray blazer and underneath a brown sweater vest over a white collared shirt topped off with a red ribbon and also a dark blue skirt, white knee-high socks and white uwabaki slippers with a sky blue tip. If the player chooses her path on Day 3, she will wear a light pink ruffled skirt with a black trim, a white shirt with short sleeves decorated with a light pink cat face on the left side of her chest and light pink trims along the edges of the sleeves. Under the shirt, two black bra straps can be seen.
Natsuki appears to be a brash, blunt, cranky, and seemingly arrogant girl at first, with a cute, softer interior as a result of insecurity, convincing Monika enough to class her as the embodiment of a tsundere. While she is impulsive and can speak without thinking, Natsuki truly cares about her friends and, even when she has obvious anger issues, doesn't enjoy fights or arguments with people. Over the course of the game, it is shown that she worries about Yuri, and, on one occasion, gives the protagonist a note asking him to help Yuri, fearing that if she spoke out then it would cause more arguments. Natsuki is very stubborn and has a hard time expressing how she feels and what she wants. When repeatedly challenged, she often becomes awkward and tongue-tied, then aggressive, and then simply bursts into tears.
Natsuki is also shown to be less pushy and more relaxed when she is outside of school, as mentioned by the protagonist when she visits his home. She is also known to be skilled in baking, as she made delicious cupcakes for when the main character first arrives in the Literature Club, and for the festival.
If the player chooses to help Natsuki for the festival during Act 1, her clothing will be a pink, frilled skirt and a plain white shirt with a cat on it. The protagonist also gets Natsuki to admit a bit of her fondness for cuteness, as he states that she can't wear this type of clothing and not be considered cute. They do baking together, and at one point the protagonist eats some frosting that was on her finger. She immediately burns up, and claims "You really shouldn’t do that kind of thing to girls...unless you really like them...” and when the main character questions her, the topic is immediately dropped and the two go back to making cupcakes. They also meet up in front of the protagonist's house, and Natsuki puts her face close to his, but they are both interrupted by Sayori, and she makes her excuse and leaves shortly afterward.
Natsuki's cute interior also involves a love of manga and anime, particularly those in the slice-of-life genre, and baking. She has been known to store her manga collection in the Literature Club out of embarrassment; another reason (hinted at) is because her father would be angry while the rest of the club obviously knows about her interest, and she is still hesitant to talk about it. Natsuki also likes cute things, such as cupcakes with cat faces, and prefers poems with cuter, happier words, though her own poems are still about sad things, such as being persecuted for the protagonist's hobbies.
Natsuki believes that it's important to be able to express something deep with few words. Her simplistic writing style puts her at odds with Yuri, who has a more extravagant style. In Act 1, the protagonist is tasked with siding with Natsuki, Yuri, or asking for Sayori's help after an argument between Yuri and Natsuki regarding writing styles. Choosing Yuri will cause her to be offended, and the player attempts to read Natsuki their poem, Natsuki will immediately shoo them away. If the player calls for Sayori to diffuse the situation, Sayori will compliment both Yuri and Natsuki on their writing and capabilities. The argument will dissolve afterwards and both Yuri and Natsuki will be satisfied with Sayori's response. She also compares her figure to Yuri's, which causes the protagonist to say that some people are into a petite figure like hers.
Natsuki hates being called "cute," even when she acts as such or does cute things, and she will deny any claims from others relating to this; nevertheless, she is much more comfortable exposing her sweet side once she knows people aren't going to tease her about it. Natsuki hates it if she isn't taken seriously, whether it's her writing, her hobbies, or just her overall demeanor. It is likely she learned to be ashamed of herself and her hobbies because her classmates judge her and because of her implied abusive father, making her abrasive nature a coping mechanism. This is also implied in a secret poem, "Things I Like About Papa", which is most likely written by her.
It is shown that she is a very lonely person who desperately craves affection. One example is during the third poetry-sharing session: if Natsuki has liked all the player's poems to date, she outright asks the protagonist if he thinks her poems are the best, which quickly shifts to her begging him to say they are, even if he hates them.
During Act 2, if the player writes a poem for Natsuki, the protagonist will read manga with Natsuki, and during the middle of the session, she will fall asleep. The protagonist will try to rouse her, and she will glitch out, with a mass of black glitches covering her eyes and mouth, and her dialogue will be distorted. Monika will find them and ask if she's okay, to when Natsuki doesn't respond, Monika will throw her an energy bar for her to eat. Monika then tells the player that Natsuki is malnourished, which could possibly be due to her father. This can also be the reason for her lack of height and her small body.
Act 2 also displays a more possessive Natsuki, as shown in the scene when she argues with Monika over getting new members. She doesn't have a lot of places that are safe for her, so when she does have one, she prefers for it to be unchanged.
If Natsuki is written another poem in Act 2, Natsuki will show immediate jealousy for the protagonist spending time with Yuri. She will show the main character her poem, which is written in Base 64. She will then start asking the player if the player just wants her to suffer, and telling him that he should stop hanging out with Yuri, and to spend time with her instead. A distorted version of "Okay, Everyone!" will play, and Natsuki's eyes will become a mass of black glitches, and blood will rush down her face, to resemble crying blood. She will then yell "PLAY WITH ME!!!" and her neck will snap abruptly, and will rush towards the screen. The screen will now show a black screen with the word "END" on it. However, when starting up the game once more, there seems to be no lasting consequences from that scene, with Natsuki still intact and the Literature Club seeming mostly normal.
After Yuri's suicide, she comes inside the club, and finds Yuri's decomposing body. She will yelp loudly, scream, then vomit all over her uniform and run away. Monika then finds Yuri, and will quickly delete Yuri and Natsuki's files. Monika eats a cupcake made by Natsuki, except her name is jumbled up and distorted. Monika will then begin Act 3.
- It is implied that Natsuki has an abusive father, ranging from emotional abuse in Act 1 to extreme physical abuse in Act 2:
- Natsuki prefers to stay at the Literature Club rather than at her home and is visibly worried about fading into the background if more people were to join the club, even asking Monika to let her know in advance if a new member joins.
- Natsuki implies that her father finds manga childish and fears what would happen if he caught her reading it.
- The father wants her home no later than a specific time.
- Monika's alterations to Natsuki's negative traits in Act 2 intensify her fathers abusiveness, evident by Natsuki's bolded "My dad would beat the shit out of me if he saw this" comment and Monika's "guess" that Natsuki's father does not give her money or lunch as she departs to school, resulting in her malnutrition and short stature.
- Related, Natsuki passes out in the Literature Club room, prompting Monika to give her a protein bar, saying it happens often enough to have Monika keep one in her bag in case it happens again.
- Natsuki's insecurity being the fuel to her tsundere archetype and boastful attempts at superiority as she looks for approval and jeers from others without being laughed or mocked at, a common symptom for victims of child abuse.
- Another circumstantial point, but if the player writes poems for Natsuki in Act 2 the day before and the day of the festival planning, then the interaction between Yuri and Natsuki changes on the day of the festival planning and takes a darker turn: Natsuki apologizes for being so aggressive the day before and leaving the club, and Yuri responds that "Nobody cares. Why don't you go look for coins under the vending machines or something?" Natsuki is shocked and angry at first and tries to speak, but instead she runs out of the club room crying. Despite this, the rest of the events for that day proceed as usual, and Natsuki will still give the player her "poem" about trying to help Yuri, stating that she doesn't trust Monika. The jab by Yuri though further alludes to the possible fact that Natsuki's father doesn't give her lunch money and thus encourages the concept that Natsuki's father is abusive.
- Theoretical at best, but by connecting the symptoms of insecurity from real-world abuse victims and how such relationships tend to begin, Natsuki pressuring to go home for dinner after saving her appetite, feeling insecure about her underdeveloped size and stature, and she boasts on about how she can overcome such a flaw with minor acts of feat, the father is likely critical of her stagnate growth and wants her to eat all provided meals so his efforts are worth the fortune that Natsuki does not become more dependent on him and become a greater drain on his resources, time, and energy.
- Natsuki's version of "Okay, Everyone!" involves a much simpler tune consisting of a recorder xylophone duet, though it is slightly off-tempo, representing her childish and simplistic nature.
- Her poems are usually the shortest and most "childish" of the group, with playful and simple music, contrasting with the messages of her poems, which are usually more hard-hitting and serious.
- In the manga Parfait Girls, Natsuki's favorite character is a girl named Minori, who she claims to be particularly unlucky.
- Dan Salvato has stated that he wishes he could have added more content to Natsuki's character.
- Natsuki is the only girl who does not have a death scene.
- Natsuki snapping her neck to the side during her corruption in Act 2 could be disputed as Natsuki's self-destruction, but the act has temporary and inconclusive consequences.
- Natsuki is the only female character whose bangs are swept to her right rather than to the left.
- The sprite of Natsuki throwing up may have been inspired by "vomit-chan," a famous Yume Nikki fanart that features the player character, Madotsuki, throwing up.
- Natsuki's file can be changed into a .png file, inverted, and then put on a cone to show a neon blonde woman with no pupils.