The Regressed Demon Lord is Kind

My whole life, all I wanted was power.
I churned the world into rivers of blood and eventually gained the title, ‘Demon Lord of Strength’. However, all this became useless when I lost to a party of heroes.
But what can a loser say? As I laid dying, I was forced to listen to the hero’s gibberish:
“If you are born again, I hope that you will live a kind life!”
But huh? When I opened my eyes again, I was back in the past.
“What do I have to do to live a kind life?”
This is the beginning of an ex-Demon Lord’s journey to live a ‘kind’ life.