Scarletine

Crafted using techniques only found within the Scarlet Sun Empire, scarletine is a steel alloy that's purified and folded over a million times and quenched with a secret substance, rumoured to be dragon's blood. Scarletine is considered quite light and is thus used mostly for blades. A well-forged scarletine blade could slice through ordinary steel if wielded by a capable swordsman

Keiko Matsumori has a scarletine katana, but because she is so bad at polishing it she often cuts herself whenever she tries to sharpen her blade.