After re-reading Chapter 582 of Naruto, I came across the new Uchiha kinjutsu called Izanami. Supposedly the partner of the Izanagi kinjutsu, this one has the power to “decide destiny” at the cost of losing the eyes’ light. Since I was hoping they’d reveal it in chapter 583 but they didn’t, here’s my thoughts on what Izanami could be:
Izanami lets the caster turn his desired outcome into the DEFINITE outcome. Izanagi was revealed as a self-cast genjutsu, which blurs the barrier between reality and illusion for the caster. In that moment, the caster is in a state of controlled existence (much like Schrodinger from Hellsing, except that you cannot disappear and reappear at will). You can say in a sense that, Izanagi gives you infinite “continues” for the duration of spell; these infinite “continues” are what enable an Izanagi user to “change” his fate.
Izanami on the other hand, could be a genjutsu that allows the caster to manipulate probabilities in order to meet his/her desired outcome. Although this may seem absurd at first since one can plan ahead the steps necessary in order to achieve their intended outcome for the target, there is still the factor of uncertainty and chance of failure.
With Izanami however, there is no factor of uncertainty or error margin because the caster is controlling these very factors. He/she is given the power to “decide the destiny”; the outcome that he/she has in her mind is what all the current factors, certain or uncertain, will lead to. This control of probability not only covers the external ones (nature, weather, time, etc.) but also extends to the people’s actions under the spell. Someone being targeted by Izanami will do actions that will definitely lead them to the caster’s desired outcome.
It is somewhat similar to Uchiha Shisui’s Kotoamatsukami, in the sense that the target cannot feel that they are under a spell and think that they are acting on their free will. The difference is that there are no memory replacements being done, only manipulation of the probability that the target will do something at a given time under the spell’s duration.
In summary, Izanami lets its caster control fate itself; anyone being targeted by it has no chance of escaping his/her end, simply because chance itself is under the control of the caster.