I promised Mandy I would find out the guy's name, so I went and tried...for half an hour before figuring it out.
STEP 1
Browse through the Jan 2011 Duet, Wink Up and Potato to try find the Jr group he is in.
Failed.
STEP 2
Google for Arashi backdancers.
Failed.
STEP 3Search Yahoo Japan for Japanese accounts of Arashi backdancers.
Failed.
STEP 4
Recalled seeing the guy on one of the Christmas greetings video in the Johnnys Family Club, and that people actually ripped Arashi's message from the J-web (a different version, but filmed on same day), so searched for the J-web and tried to find that guy's video.
Succeed.
To watch the group, go
here. Click on the "Johnny's Christmas Message 2010" banner on the right sidebar. Click on the gourd-like ornament on the bottom right of the Christmas tree (hover over to see if it read "They武道").
Yeah, from that group. What's with the name....And they're not featured at all in the YE mags. Meaning, they aren't an established group?
So, basically, it's this guy:

What's with him huh?
Well, there was this part during the 21 Nov concert I went to where the members were all quite far away attending to the stands fans. And just nice, two backdancers were dancing on the hanamichi in front of me. The two in that picture. So, since I couldn't see the boys clearly, I just looked at that right hand side guy dance. And then. He blew a kiss at me.
O.O
The odd thing is, due to the high tension and excitement, I actually felt my heart stop when he did that!
=.=''''
If only it was Nino or something!!