When we first meet Ringo, while he is still working at his father's restaurant, there is a brief shot showing the knife he is using to cut the soba noodles (a "sobakiri"). Mizu's "kakihan" (aka maker's signature) can be seen on the blade.
Mizu's katana hilt is covered in rayskin but lack the silk wrapping over it. Which means the katana isn't quite finished yet, and that its owner might have set on her course before she was actually ready.
Cary-Hiroyuki Tagawa, who plays The Swordmaker, also played The Swordsmith in Heroes.