Kai, Japanese-made razor blades, have always been considered direct rivals of Feather razor blades.
Kai blades are made of high quality stainless steel, and are also used in the medical-surgical field. Extremely sharp (but less than Feather), and sufficiently indulgent.
The duration of the edges appears to be average.
Quantity of blades in each package: 5 blades individually wrapped in waxed paper.