Mist. The whole Yagura reign is so mysterious. And why the hell were they tracking down Rin? And how did the powerful 7 swordsmen of the mist all just drop like flies? AND WHY DID THEY HAVE A KEKKEI GENKAI GENOCIDE? The world may never know...
I'm going to say the hidden Lock from that filler episode. They survive solely on stealing intel and blackmailing other villages into leaving them alone.