On the other hand, there is a similar appearance called "mukade-shinae". It appears in blade surface like wrinkles, not cracks. It not a flaw. When a blade is heavily bent and straighten again, it appears on the blade surface. It is very thin wrinkles on the steel surface, so it can be removed by sometimes polishing.
http://www.ksky.ne.jp/~sumie99/flaws.html