I'm not sure about the exact plot as I haven't read it in detail. But generally, it might be about a hero who decides to stop fulfilling the role of a hero, perhaps due to some disillusionment or personal reasons.
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.
Since I haven't read the 'I Will Quit Being the Hero Novel', I can only guess. There would probably be the hero himself who wants to quit. There might also be some friends or comrades who try to persuade him to stay in his heroic role, or who are affected by his decision. And there could be some antagonists who either oppose him because he's a hero or who take advantage of his decision to quit.
It could be that you faced an overwhelming enemy or a situation that made it impossible to continue as the Demon Lord. Or maybe you just wanted a simpler, more peaceful life.
Well, sometimes we simp over fictional characters because they give us a sense of comfort and entertainment. Their adventures and personalities can be more exciting and interesting than what we encounter in our daily lives. Plus, we have complete control over how we imagine and interpret them in our minds.
Not necessarily. Having a deep appreciation for a fictional character is common. It becomes a problem if it starts interfering with your daily life or relationships. So, assess how it influences you.