The Trial Sword (試しの剣, Tameshi No Ken, translates as Sword of Trials; The Trial Sword in the English Dub) is a weapon that Suzuki made from a tree in Spirit World.
The Trial Sword is a normal looking black and light gray sword handle. When used by Shishiwakamaru it can be opened from the middle revealing a fleshy skull. There's no noticeable change when in use of Kuwabara, only forming a multicolored (as a sword) or magenta (as a flyswatter) spiritual energy blade similar to his Spirit Sword. Appearance may differ from user to user.
Dark Tournament SagaEdit
Kuwabara uses the Trial Sword to defeat Elder Toguro.
Chapter Black SagaEdit
However, Kuwabara mentions it early on during the Chapter Black saga, when he thinks that the reason that his powers were disappearing was a side-effect of the Trial Sword.