Ver Ka means version Katoki, name after the guy who design it; Hajime Katoki. Ver Ka are for those redesign by katoki, for example wing ver ka is a redesign of the wing tv series by Okawara, RX78 ver Ka is the redesign of the original granddaddy, etc etc. There are those that originally by katoki like ex-s so there is no ver ka attach to its name.

Some may not have a significant difference between the original and redesign ver ka version while some totally different from its original design. From a model kit perspective, ver Ka often includes a crap ton of decals and better proportions/looks but are often very fragile.

Any reason why zaku marine need to have some sort of breathing equipment?