My Opponent Is Utterly Defeated!

I'm getting ready to return to my comfort zone and make up the world-destroying trio. In a nutshell: "A mad scientist villain who destroyed the world has a change of heart in his old age and decides to travel back twenty years. I stop myself." [Short Blurb] Shan Ran meets a man who claims to have come from twenty years in the future. He tells him one piece of good news and one piece of bad news. The good news: "In twenty years, you'll become one of the world's leading scientists, and while working on a project, you'll accidentally develop a time machine." The bad news: "Someone used the time machine to come back to the present, twenty years ago, to kill you." Shan Ran looks at the man: handsome and aloof, with deep-set eyes, ruthless and sparing with words. He voices the question on his mind: "So are you going to kill me, or help me?" The man grips his collar and gives him a vicious smile. "What do you think?" * A narcissistic romance: two people bound by fate, in love and at war, constantly getting on each other's nerves, with the emotional maturity of grade-schoolers. Honestly, who can stand their former self? Going back in time and not putting yourself out of your misery is already the truest love imaginable. The love interest is stronger than the protagonist, naturally. He's the protagonist from twenty years in the future. If he weren't stronger than his younger self, what would have been the point of living all that time? Back then, he was lost too, with no one to point him in the right direction. So he went back to that time to show himself the way. Theme: Has the world not been destroyed yet?