a net friend of mine linked me to one of her favourite videos --> http://www.youtube.com/watch?v=dHEtZNI4Ynw
I watched it and fell in love with the background song... The song is by Kanjani8 --> B.J. from their 8th single "Wahaha"

I found the lyrics of this song too, with english translation...
http://goro-chan.livejournal.com/103893.html?view=292821#t292821
Thanks, Goro-chan for taking the time to translate it...