Another Naruto idea, but I haven't fleshed this one out very much yet. I came across the idea in another fanfic called "The Quiet Fox" by TheBeardedOne, though he simply uses the English name: Eye Debt. The idea is similar in practice to a life debt, however it is specific to rescuing a Hyuuga clan member from a situation in which their Byakugan would be stolen from them, thus keeping their secrets safe. Although TheBeardedOne uses this for the Hyuuga clan, the concept could be applied to the Uchiha clan as well. It is an interesting idea that is worth exploring in the future.