To those of you who are easily offended, I want you to be aware that I love this show/manga and all of the characters (yes, all of them). Like an elementary school boy, I show my love by making fun of it. So if you are curious to know who are my favorite characters, all you have to do is check is how often I make fun of them.
If English isn't your first language you might want to be careful, I throw a lot of puns and brick jokes. If you are not familiar with basic Japanese fan culture, other jokes may not make sense to you. But if you have great spelling and grammatical powers, please utilize them! I don't care if the mistake is small, I want to improve any way I can! Yu Yu Hakusho belongs to Yoshihiro Togashi, last I checked.
Case Number 01: If Kuwabara was a Girl...
She would've been envied by the boys and constantly mocked by the girls at school for her unusual height. She is a tom boy at heart, and keeps her hair short so no one can use it against her in a fight. If that mess of curls on top of her head was natural in the original, then here she would probably give that Shirley Temple look. Since she's big height wise, she's probably big around her chest area too (I'm considering anime physics, not real life here). And because of that, her three unnamed school friends would constantly dream of being 'more than friends' with her.
She would wear proper school uniform, but as soon as she was out she would be wearing pants. In an ironic twist, she still would never hit a girl, despite being one herself. Yusuke would call her a hypocrite (if he knows that word), and another fight would ensue. And no one would mock her love for cats. Fan service might feature her in a cat girl costume and people would call it adorable.
(For those having issues imagining it, you have to remember that Togashi can only draw pretty girls unless they are old. Then they are just awesome.)
As for the fandom, a lot less people would find her annoying. Because she's a girl, she would then be compared to Botan and Keiko and not the supreme power houses (read: Urameshi, Hiei and Kurama). She would never be called a useless git and would be seen as a great helper who actually does stuff.
For relationships in the show and manga, she would start with a love triangle with Keiko over Urameshi and end with a love/hate relationship with Hiei. In the fandom, some people would consider Keiko boring compared to Kuwabara and would hold a dim candle to the pairing that 'should have been'. Meanwhile in another part of the fandom, there would be a redhead battle over Hiei/Kuwabara and Hiei/Kurama. Some of you might try solving it by going Kuwabara/Hiei/Kurama. Other might rebel and go Hiei/Kuwabara/Yusuke.
Or, keeping to her original character when she was a male, she would be the star butch lesbian. In fact, since Yukina is an Ice Maiden and so probably isn't so hot into men to begin with, she would jump right into Kuwabara's arms.
Oh yeah.