@Raspberry Plum because out of all heroes that appear in that world, Kim Min Su is the strongest, in early years of his regression, Kim Min Su is part of hero who prevent and fight other heroes that want to destroy the world. After hundreds of regression, the regression heroes realize what he need to do, which to create a devil king that can finally kill him , but all of it failed as Kim Min Su always able to defeat them and finally the regression hero realize that Kim Min Su is the one he should make as devil king.However, the regression hero goals not for the world destruction, but to cut off the ties of others life and fate with him due to him unable to die properly and will always went back to the day he come to his world after defeating demon king in another world. So after his death, he need to ensure that the demon king (Kim Min Su ) will be died and hemce the reason before he went to his death, he trained the spear and help othere heroes to able defeat Kim Min Su