Blue Turtle Knives

What is this thing?
Hollow & convex ground Japanese chef knife. Never seen anything quite like it. This big boi is over 1/4” thick! Very odd to sharpen I convexed the top then hit the back side on 1k & 6k Japanese water stones.

This ones available, no sheath cuz I don’t have shop access atm. L6, green micarta, handle on the larger side. Small cat approved!