Board Thread:Questions and Answers/@comment-36.73.74.173-20150908162432/@comment-26222562-20150908181246

World 1 and 2 have their Kebiishi appearance rate lowered to prevent the game from getting too hard for newcomers, so it's quite understandable that they have never appeared for you. However, if you constantly grind on the map they will eventually come :)

Alternatively, you may try infecting maps on world 3 onward.