All you need to do s fire the cannon at the cannon firing at you from the other side,then
roll the ice through the door and use it to freeze the hot rolling fireballs.get the key
from the platform and Viola!

The answer above this one is exactly right.

Yes, as the first answer is, I completely agree. That's all you have to do.

Use Veil of Mist to slow time down and Power Slash the purple ball to send it flying to
the cannon. By the way, dig up the chest under the cannon on the left (at the very first
room in Wawku Shrine) to get a Stray Bead. The other one holds the Ruby Tassels.