I've actually been pretty curious about that too. When I'm sparring with Terumi I tend to go in with my left hand, though I'm right-handed. It's because of this.

[He holds his left hand out, palm up so she can see the tattoo there. It's been weeks and yet it's still in great condition! How the hell does that happen, idk anime germany.]

So I'm used to fighting with this array, but I still don't remember getting it done.