Shadow skill is, as it's name implies, a type of skill. There's front skill, and Shadow skill. Shadow Skill uses a lot of kicks because it was something made by women slaves that don't have a lot of strength in their arms. And even if they did, their hands were tied, so they needed a way to fight back. Normal (front) skills wouldn't work, so they made up Shadow Skill. Both Elle and Gau say "My shadow skill is invincible!".
As far as Medaka goes, I never read the one shot. And I took over in the mid 20's I think. I didn't really read everything prior to where I took over. But I didn't mind how the story was developing. Mostly because it wasn't the same old shit in a different toilet.
Yeah, he had a little sister... that series had the potential to be great, but screwed up badly! Man, I hope Veritas doesn't go down the drain like all the other (though not many) manhwa I've read.
dna11, I checked out ace... it was good, but not good enough for me to try and commit time to translating it. Sorry, but you'll need to ask somebody else.