There are many types of powerful weapons in "Beast of Reincarnation," and the Roaring Shark is one of the most useful. To obtain it, go to the teleport point at the entrance of the Bridge Control Room in the Fuji Border Area of the Mountain Region. The Roaring Shark sword can be found right next to the teleport point.
How to Obtain the Roaring Shark Weapon in Beast of Reincarnation