Seasplitter (also known as Wave Slash) is a sword skill which first appeared in Dragon Quest: The Adventure of Dai as a creation of the hero Avan. It made its game debut in Dragon Quest XI as the ice equivalent of Gigaslash, slicing through a group of foes with a blade of freezing water.
Wave Slash is the second of the fundamental techniques of the Avan-style sword school. It launches a blade of compressed wind from the user's sword to strike from a distance, which is capable of cutting through amorphous things like flames and water. Hyunckel also notes it to be the school's fastest technique, making it useful against speedy enemies.
Seasplitter is learned by speaking to the elder of Havens Above in the game's third act. The Luminary must be equipped with the Sword of Light or one of its upgrades to perform the technique, and it will deal up to 210~250 ice damage to one enemy group for 16 MP. If the player has completed quest #60 then the base range will be raised to 200~240, and the limit up to 400~440 for 32 MP.
Wave Slash can be learned by Dai at level 32 and costs 58 MP to use. It inflicts 250% Crack-type physical damage to all enemies in a range of three squares in front of the user. Wave Slash's potency can be increased another 20% through Talent Blossoming.