The Frozen Skein is the Bloodline Limit of the Mori clan of Kirigakure.
It is a poorly-kept secret among the most erudite of shinobi that those clans with natural affinity towards pure Yin chakra - with its associated concepts of stillness, complexity, perceptiveness, and reserve - possess substantially elevated intellects relative to the average population. Why, then, do they not rule the world? Along with that poorly-kept secret is a well-known admonition: that the costs of a Yin bloodline almost unfailingly outweigh the benefits. The Yin is associated with the abstract and the mental, but it exists in balance with the Yang for good reason. Should it pre-dominate, its negative associations will prevail in greater measure than its positive - which only makes sense, as negativity is itself Yin-associated.
A prominent example: The Nara of Konohagakure. Intellectual titans, crippled by an almost immeasurably crushing laziness. Every scion born has the potential to be a Kage, and yet that potential will likely never be realized.
The Yin-natured clan of the Hidden Mist does not carry as heavy a burden, or as great a gift, as the Nara of the Hidden Leaf, but they are similarly beleaguered. From the Leaf the Yin stole motivation, but from the Mist it stole initiative. Members of the Frozen Skein are virtually unable to create original plans of action beyond the fairly basic. Furthermore, while they are able to critique and adjust plans proposed by others, they are far better at neutralizing flaws than contributing constructive improvements. They can salvage terrible plans, but are basically useless at improving already good plans. This is exacerbated by their retiring nature. They much prefer to act decisively and adjust a plan as it is executed rather than critique a plan to its creator’s face, though this can be overcome with time and socialization.
Within the desperate straits of a missing-nin’s life, where every decision counts and every action is full of pitfalls, the Skein user is in their element. Though they still need a team to function correctly and propose plans of action, they can be argued to be the most critical member of any team.
*A Frankly, Terrible Idea: The precise, well-timed movements and words of the Skein can turn a catastrophic plan merely bad, and some bad plans barely adequate. This is typically resolved narratively, but if a mechanical resolution is called for, their adjustments can offer an impressive (usually +2d) bonus when against utterly overwhelming odds, and a significant (+1d) bonus against bad odds. Alternatively, the negative consequences of a failure are decreased by some margin. This ability is not perfectly consistent and may fail due to GM fiat.
*In Winter’s Grasp: The bloodline user is unable to originate any plans of significant complexity. While this does not impair them too much in day-to-day ninja life, they would find it extremely challenging to thrive outside of a team.
*Monomaniacal: Choose one Intelligence-related Skill. Its Intelligence multiplier becomes 3 if it was 1. Essentially, this is meant to represent substantial innate talent in a particular intellectual field, the original intended benefit of the Skein program.
*The Best Laid Schemes...: Once per [story], the Skein user may draw upon all his/her hoarded reserves of initiative and creativity in the ultimate expression of Yin reactivity. They may perform any sequence of actions necessary to counter one otherwise extremely formidable plan or scheme, as it reaches its culmination. For this brief, shining moment, the Skein user is every bit the equal (or even the superior) of the Nara they were created to rival.