Since I'm not familiar with a specific 'Passion Yuuji' novel, in general, a novel might have unique characters. Maybe the characters in this novel have strong emotions and passions that drive the plot forward.
I'm not sure as I haven't played this visual novel specifically. There could be a lot of different interactions between characters in a visual novel, but without experiencing it first - hand, I can't say for certain.
He might be depicted as confident. In a visual novel, this could be shown through his interactions with other characters, where he takes the lead in conversations or situations.
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.