It's hard to tell if he's actually holding the girl while she's 'flapping' her tail. It looks like he is, and if so, he's pretty strong (but we know that.)

There's a TV show where he's with a bunch of girls who are fishing in a big glass tank, and Gackt just reaches in and grabs a fish, lifting it up with his thumb in the fish's mouth. Maybe that's how they do it back in Okinawa - wild.