Most BSD light novels often have complex characters. Since they are based on literary figures, they bring in the depth and complexity of those original personas. For example, a character might have the same traits as a famous writer but with a unique twist for the BSD universe.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
The appeal of all BSD novels lies in their ability to create immersive worlds. They draw readers in with their unique concepts and engaging storylines. For instance, the way they handle character relationships is very captivating. The conflicts and reconciliations between characters make for a great read.
Honestly, there's no definite answer on when the BSD manga will end. It all comes down to various factors like the author's inspiration, the popularity of the series, and the publisher's decisions.