The island is where the legendary Shichiseiken, a cursed blade, was sealed. Every one hundred years, there is a red full moon that increases the sword's power. Several hundred years ago, three princes fought over the love of a priestess which led to a great war, which is what cursed the sword in the first place.[1]
The sword forced the peoples' rage to increase until the priestess gave her life to seal the sword. The island is also the location of a Marine dojo, and there are three towers connected by a cave that are used to seal the sword's dark power. The sword was destroyed by the Straw Hat Pirates.[1]