Youkaiittou

This sword is passed down through the main family of the Youkai Clan. It is currently owned by Karasu Youkai.

This blade is far from a normal one, and has even been called a demon sword before. When the owner of the Youkaiittou dies, whether the sword is currently with them or not, all of their chakra is absorbed and stored inside the blade, giving the next user access to their chakra. This blade has been passed down through dozens, if not hundreds of generations, meaning that it has a massive store of chakra that Karasu can access and use at any time.

The sword itself can be used by just about anyone, but access to the sword's chakra is only permitted to a member of the Youkai clan's main family. This means that if the sword is stolen, it'll be little more than just a very sharp sword that's hard to break.

Also, despite the sword's immense powers, it looks like a fairly normal sword.