How do you get the fire sword on phantom hourglass

all you have to do is get ten power gems to get your sword fully flamed! wisdom gems will get your shield to be stronger courage gems will let you use electric shocks each time you swing your sword by: messenger boy! peace
You should get all twenty to make them stronger. Yes ten will get the sword full of fire but all twenty power gems will make it stronger  The top are exacly right! You'll have to go to an island that offers up those power gems. The red ones was it? That one is supposedly make the red fary that you rescued stronger. When you pick him from the status screen and change from yellow fary to red fary your sword will be on fire. But only if you had given that spirit 10-20 gems.