Reading through Yu Yu Hakusho fanfiction in hopes of fanfic recs, and people, please: Kuwabara Kazuma does not have a happy home life.
Now, this is mostly based on assumption, as I haven’t read the manga all the way through, but Kuwabara’s the school delinquent, you never see his parents, and his sister is very hard on him. My impression is that she basically had to raise him by herself, possibly with absentee parents. Imagining a young Kuwabara being trained by his father to fight a tiny Urameshi Yusuke is nice and all, but it’s more likely that they didn’t know each other till middle school. Kuwabara would have grown up on the rough side of town, and that’s how he learned to fight. It’s possible he was top dog in his area for a little while until Yusuke crashed his party. Seeing someone so much more powerful than he was challenged his honor, so he made beating Urameshi a life goal.
That’s how I see it, anyway.