This boss took me FOREVER to understand how to defeat him; I almost gave up on the game. First stand behind the pillar/tomb to avoid the arrows easily. Then stay there until Stormraven comes down his hill and build up your green gauge/meter by blocking his attacks. Then lure him around the tomb and do in sorts that he hits the pillar with his axe instead of you. Just stand behind it or around when he is about to use his big attack. If done correctly (it doesn't always work, you may have to try several times) his axe will get stuck in the pillar and this is your cue to use a special attack to hit him. Then start the whole thing over again until he is defeated.