Mizuho
Mizuho was a Japanese company that made the Mizuho Six 6×6 folders in the 1950s. According to this page at Japan Family Camera, its full name was Mizuho Kōki Seisakusho (ミヅホ光機製作所) and it later became Neoca. This name was translated as Mizuho Optical on some body engravings.
Its logo was MKS in a stylized lens scheme. On a box for a Mizuho Six, observed at a Yahoo Japan auction, there is MIZUHO CAMERA IND. CO,LTD.
Note: According to this AJCC page, Mizuho was written ミヅホ on period advertisings, not ミズホ.
