This can be done in a local match or online public match.
How to do a Fierce
From 1P side. Right, Down, Down+Right+LB
Best advice would be to remap the Fierce button. I personally remap it to X just for this achievement.
Hope this helps aside the other solution
Remeber a Shouriken is a Punch not a fireball.
It may Help its something like a Z Motion on your controller. Also you can try to use a double quarter circle, which sometimes works.