A lot of authors and mangaka really need to learn that tragic backstories isn't some magical "get out of jail" card that you can attach to any villain to add depth and have your audience feel bad for them.
There's a lot of ways to do it well, but you can't just create a hate-sink character designed to be as unlikable as possible, have no foreshadowing that they aren't anything other a two-dimensional asshole character, then suddenly drop a sobstory on them out of nowhere and expect people to feel really bad for their villain.
This guy isn't even the first, I've seen so many authors try and do this with their villains, only for all their readers to go "yeah who cares, just die already".