A Brave Father from Another World Defeats the Devil on His Behalf

I have wanted to write a brave story like this for a long time. I wonder how many people have had such a dream when they were young? I don't want to make the protagonist invincible because of the system, so in many aspects I don't want to give him a fixed panel value, such as a health bar. Life is a long road, won't you feel bored and lonely after a moment of invincibility? What I hope most is that someone can give me some advice. Brave warriors are not the type I am familiar with. If you can't take into account all aspects, please feel free to put them forward.