cobalon:

— Reshiram has a jet engine-like tail, which it uses to accelerate itself when flying at high speeds. It can send flames from its tail into the air to incinerate everything around it. By flaring its tail, Reshiram is capable of moving the world’s atmosphere and changing the weather. This tail generator is also activated when influenced by either Fusion Bolt or Bolt Strike, which in turn powers up Reshiram’s own Fusion Flare or Blue Flare. In Unova mythology, Reshiram sided with the older brother who sought the truth. As a result, it firmly believes in truth.