The Tidebreaker

The Tidebreaker appears as an Oak staff that is imbued with inset silver designs adorning it in complex nautilus shell patterns. The Tidebreaker is one of the artifacts that is lost at the start of the story.
The Tidebreaker has the power to control water. The most powerful wielders are able to part seas, like in the military campaign against the southern Forrest Kingdom. The Tidebreaker can control water in all forms, similarly to water benders in Avatar, and can even pull moisture from the air in order to produce water to fight with. The Tidebreaker is, like many other artifacts capable of using its power in a wide and diffuse manner, or a focused and powerful manner.
The Tidebreaker can cause great storm surges, flood valleys, and dam rivers temporarily as shows of great force. It can also finely manipulate water, forcing water away from someone's head, allowing them to breathe underwater, or precisely move water from one vessel to another.
The former wielder of the Tidebreaker was leading the military campaign against the Forest Kingdom which occurred shortly before the story, between the time of the Thunderspeaker rebellion and the present day. This fight was ill-fated for the Altier and the Zodiac, resulting in another devastating loss for the Altier. This conflict resulted in the Tidebreaker becoming submerged at the bottom of the inland sea that divides the Forest Kingdom from the mainland. The family that is the rightful inheritor of the Tidebreaker continues to put on a show of force in front of the rest of the Zodiac, but everyone on the council knows that they do not actually have any power. The Zodiac does, however, preserve the appearance to the outside world of power, as they do not want the people of Altier to know that the Tidebreaker has been lost, weakening their empire.