Bad blood. That's all there is to it.
The sheep herds Mother brought here with her- they're too inbred, now. We need new sheep. Which- well, it won't be a problem for quite some time, I suppose, but. A sheep only lives for ten to twelve years, maximum. We've been eating more lambs than usual- they're being born… defective.
Clan law states that all sheep available to breed must be within thirty percent of conformation. There are various strains of wool that come in and out of existence over decades; the conformation standard ensures that all the recorded wools stay within the bloodlines.
Yoi Hyaku, the good hundred, live just past some of the densest forest up here on the mountain; there's a wide range of terraced glades that they live out in, covered over in wildflowers and lush green grasses. They produce the majority of our trade wool, and what we base most of our basic, training weight fabrics on. I'm actually quite proud to say that, in Konoha, quality wool comes from us- we make the finest specialty wool, and the people down in the lowlands know quality when they feel it. So far, they've shown the least deviation. Conformation in that herd has always been particularly good, and… if I have to merge the flocks together, the Yoi's will be able to hold the bloodlines for a while yet. Their internal management is particularly stringent- there are very very few non-conformation lambs born to the Yoi. But there is a concerning and marked rise in the number of non-conformation sheep being born.
Shio Hyaku, the salt hundred, roam out on the cliffs of the mountain; they tend to graze on brambles and roughage we cut from the Terraces past the forest. That flock is where Irontooth and Stricker come from- Slink too, for that matter; it's what my coat is made of for the most part, and my coat wouldn't be so very waterproof if Slink wasn't so oily and tough and so easy to weave tight like fishscales. The Shio's actually tend to associate strongly with the Yoi; conformation standards for the Shio are loose, compared to the last flock.
Tou Hyaku, the tower hundred, are a flock of sheep numbering nearly always at twenty five monogamous couples. Their current matriarch, Ojo-hime, controls the lambs born to that flock with steel shod hooves. However, she's only got about eight more years left in her- she's two years old if she's a day. Her successor, Kaiju-hime, is sweet- but moronic. She is not smart enough to manage the flock like it needs to be controlled. There are, so far, no non-conformation lambs that have been born to that flock. The wool that comes from that flock is the source of my sealing ability. Their wool has a specific characteristic of being able to hold and release chakra in a controlled manner in its base state; when spun or woven, it's effects can be further refined.
Yayoi was very clear that since Raiko couldn't handle the sheep due to… safety concerns, I would have to. My personal ambitions must be secondary to the clan's wellbeing- in this, we are quite agreed.
Therefore, before I turn eighteen, I must secure new bloodlines into the Iga sheep flocks- new blood for the Yoi, the Shio, and the Tou. I will give myself six years- I'm ten now, so in six years I must be strong enough to journey to the land of Demons, far to the west; I must go to the fallen halls of my ancestors and entice the sheep that yet remain there to return with me.
May the Three see fit to help my endeavor.