Yes, the Beastars manga has come to an end. It left fans with a memorable and impactful conclusion that tied up the various storylines and character developments.
Another theme is her self - discovery. In the show, Sugar had her own insecurities and dreams. Fanfiction may focus on her journey to find herself, whether it's through her singing or her personal growth. For example, she might overcome her fear of not being good enough. This can be a really inspiring theme in many of the stories.