A true simp story could be about a guy who always buys his crush expensive gifts without expecting anything in return. He just does it out of pure adoration.
It could be that their storylines and personalities offer an escape or a form of entertainment that resonates with you. Sometimes, we simp for them because they represent something we wish we had or could be.
One idea could be a rengoku fanfic where he trains a new group of young slayers. It could focus on his unique teaching methods and how he instills his values in them.