I own nothing.
An angry Edward is a flood- dangerous, damaging, deadly, but sometimes it can heal the land anew, bring life back to parched earth.
Alphonse, then, is the floodgate- the barrier to help control that flood. To help it do good instead of bad- guard against damage and direct it where it is needed, where the life is sapped from the dry ground.
But should that floodgate be damaged or broken, should Alphonse be hurt- or worse-
Then absolutely nothing in the world could protect you from the flood- from the wrath of Edward Elric when his little brother needed him.