Mostly for mystery or gore fans.
Characters that are not or not yet important to the story are only animated as shillouette.
This might be explained as an attempt in cutting the budget. But since other parts are well animated, it might be because this is a tribute for Edogawa Ranpo, a big name in Japanese mystery fiction (and ero guro).
You might be familiar with the names Edogawa or Kogoro if you have watched/read Detective Conan or kindaichi shounen no jikenbo, Nijū Mensō if you have watched/read Nijū Mensō no Musume. They are all inspired by Ranpo.
Just like in his original works, all the characters have their own 'crazyness'.
With Amazarashi's song for OP, it is even more of a masterpiece.
Explanation by Xaaron on Monday, 05.10.2015 11:33