Japan is a great county, but when it comes to censorship they are backwards as F. The things they show (tentacle penises fucking little girls) and the things they don't (some cuts on a body) don't make any sense.
Something is clearly wrong when 70 years ago Kurosawa made movies where decapitation was as normal as anything.
that's every country...
in the US violence is ok, but profanity and nudity isn't.
in most other countries it's the other way around.
all of them vary in how much one is ok over the other.
in Germany, thankfully, it seems like slowly but surely censoring stuff becomes rarer and rarer. but some extreme violence still gets censored in order to get a USK rating.
(not getting a USK rating is the equivalent of an AO rating in the US basically, with much of the same restrictions attached)
also it usually isn't as cut and dry as "decapitation = ban", and more about the context in which they happen. in AC Shadows you can run around with Sasuke and behead random civilians without any repercussions basically.
meanwhile in Ninja Gaiden 2 on 360 (which is not banned but rated Cero Z) you decapitate enemy ninjas that attack you.
In Ninja Gaiden 2 there is also way more blood and gore than in AC Shadows, but it's fine in NG2 because of the context on why it happens