The Hattori Clan in it's own was not a formal clan but a union of several warriors with the same name. Although this sounds like a clan it is very different as they all shared no reliable bloodlines but in name and this is why the Hattori are the clan we know the least about with most sources providing only a few sentences about them but we do know that this mysterious clan was very mysterious at it's time with it being a focused clan on stealth.