To write a character - driven story about Taiju Shiba, focus on his internal conflicts. For example, his struggle between his tough - guy exterior and his more vulnerable emotions. Also, show how his relationships with other characters shape him. His interactions with his siblings or friends can be a great source of character development.
Well, a plot idea might be that Taiju Shiba decides to start his own dojo to teach people the value of discipline through martial arts. This could lead to him facing various challenges from rival dojos or skeptical students. Another idea is that he travels to a foreign land where he has to adapt his fighting style to new opponents. Also, a fanfic could explore what would happen if Taiju was given the power to time - travel and he uses it to correct past mistakes or prevent future disasters.