Her Personality:

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.

Her 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.

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.

Try to think about what she might sound like in the Actual Game.

Ref: https://www.youtube.com/watch?v=jtqoPCO8uDY