Where can I find a “sakaba or sakabatou” – a katana with the cutting edge on the inside curvature?
You can’t – cartoon swords are for cartoon characters. Blades similar (called kubikiri) were made in tanto and small wakizashi size, but I’ve never heard of one in katana length. The entire premise that a concave blade is not an offensive or lethal weapon is wrong. Many styles of knives and swords have concave edges. I point to the Nepalese Gurkha and Turkish Yatagan as two of many such weapons. I suspect “sakaba” are purely the product of the cartoon world. A kubikiri tanto is pictured on the unusual tanto webpage of this site.
