Warning: Major spoilers for Rin’s route contained below.
Rin is actually a very layered and conflicted girl beneath all the non-sequiturs and impulsive actions. She cannot handle social pressure or the stress of expectations placed upon her. She simply wants to paint as she likes, but no matter the result, every audience she turned to failed to understand that exact direction she wanted them to go, making her feel dissatisfied and isolated.
She felt that she was slowly losing her own meaning and worth, as long as no one could grasp the intention of her art. She relied on art for communication, and grew frustrated when it wasn’t interpreted the way she wanted it to be. Such was the reason she kept spouting nonsense: speaking in an abstract way, like her style of painting, was the only way she really knew how to converse. While it often angered others, she felt equally bewildered: how could they expect her to be any clearer, when she herself wasn’t sure how to vocalize her own emotions, or even what her emotions exactly were. While it may have sounded as if she was joking, she was actually being as serious as possible, and yet no one could grasp her intent anyway. Trying to understand her feelings was hard enough, so she opted for attempting to not think at all.
She had expressed, many times, her absolute terror of becoming someone else. She craved to be accepted as who she was, but due to her seemingly lackadaisical thought process, she was simply written off as being superficial. She was afraid of changing, but felt that she had no choice but to change, if she was to ever find acceptance.
While the bad end, with her transferring schools to become a professional artist would normally be portrayed in a positive light, it’s made clear that trying to live out others’ dreams or attempting to live up to everyone’s expectations only has a destructive impact. In following a promising career, but with no actual ambition of her own, Rin found no genuine contentment. When she did try to reach out towards others, forcing herself to paint for the exhibit in hopes of finding an understanding audience, she ended up trapped in an obsessive spiral, neglecting food, sleep, and social interaction, becoming nearly addicted to smoking and masturbation in an attempt to find inspiration. Most frightening of all was the realization that she was actually trying to kill herself, both in a metaphorical and literal way, if it meant that she could produce results that others would approve of, as a recognized artist, even if the person she would become was no longer her true self. And in the end, it was implied she would eventually take her own life from never gaining the acceptance she needed.
In her good end, Rin realizes that she does not need to change herself for others, turning down the scholarship and business propositions to instead take things at her own pace. Whereas she previously felt unfulfilled and lonely, despite the promise of fame, the only thing she wanted in the first place was to be able to freely express herself through her art, and to be understood in turn. Hisao was the only one who was willing to even try to understand her, and through his support was able to give her not only confidence, but, at last, happiness.