Spoiler!
Kwon Yido:
This man was a textbook case of scum Alpha buying an Omega in their first life. He was made to be hated and if Seijin wasn't in such a bad place mentally after years of abuse by his 'family', it was doubtful he would have stayed with that version of Kwon Yido at all. No self respecting person would.
As always, his regret came far too late. If it wasn't for the regression, there wouldn't be any story.
In the second life, he really did try his best to make things right for Seijin. He was a gentle and caring man who arranged everything for Seijin's best and pushed Seijin to aim for his own happiness and independence. Away from him, because he felt (rightly so) that he didn't deserve Seijin.
He really got his crematorium set at the easiest level. All the bad things that happened were things that he could have easily handled if only he paid a little attention, so now that he even knew the future, they were quickly dealt with. Seijin didn't remember anything and was in desperate need of affection, so he easily gained Seijin's love and affection again, so much that Seijin couldn't stay away even after remembering their first life.