thanks for cookie spam in a request.
to define a kekkei genkai, you are right.
you might have noticed that the hidden cave never talks from "hey, get a kekkei genkai here".
it gives out outstanding abilities. therefore any POWERFUL ability with a rating to be insane to put in just like "get it now, use tomorrow" is nonsense. Whatever costs a great deal of work, will be ONLY in the hidden cave.
Note that I reserve the right to have requirements for future abilities obtainable there.