The rarity of Helm of the Raikage Warrior is Mythical. At this moment the item is available for trade.
Helm of the Raikage Warrior is a skin for Storm Spirit. The skin was added to the game on January 7, 2016, it was created by Jigglypuff.
Helm of the Raikage Warrior has been recently added to the game, which makes it rather popular with the game community.