How the wicked witch became the hero's sidekick

A witch is meant to be cruel and evil. The hero will save the princess, and she will be killed by the hero. Not with me. Transmigrated into the body of the wicked witch, I will not play this role. I will look at the story from the side and do nothing. 
But why is the hero lying half-dead before my doorstep? A place he should never be. With a story out of control, I have to give the hero a helping hand to secure the happy end of the story myself.

Follow the story of an isekai'd sarcastic witch who chooses to become the sidekick of the hero instead of his enemy.