I couldn't really find a perfect video to portray Ryuu...but if you meshed these two from Soul Calibur it would fit his style pretty well. 

Give Natsu a longer blade and you have his basic movements. Though the lightning moves would be more fire. 
[youtube]d5J1s5Z0wh0[/youtube]

With Mitsuruugi being his Finishing moves.
[youtube]jn-AmGryChg[/youtube]