Byakugan

The Byakugan is a kekki genkai of the eyes that genetically belongs to Clan Hyuuga. Anyone who is capable of using the Byakugan can see almost anything they wish to see with it.

Weaknesses
As great as it seems, the Byakugan has one weakness. At a certain point on the back of a Byakugan-user's neck, there's a blind spot. Anyone who manages to launch a projectile aimed directly at that particular point can evade detection, which may lead to the user's death.

However, not many ninjas who fought Byakugan users manage to figure out this weakness in time.