Board Thread:Questions and Answers/@comment-30084321-20170124175038/@comment-84.188.230.198-20170124191908

All swords have a fixed drop rate from the Kebiishi, so it doesn't matter in which era/map you're fighting them. Whether you get your desired swords or not is up to RNG.

In any case, good luck obtaining Higekiri and Hizamaru. :)