Through most of Rokugan’s history winter has brought an abrupt end to war. The costs of waging war in the bitter cold and snow are simply too high, and every time it has been attempted the army responsible has ultimately been defeated. This did not change until the Empire’s twelfth century, when the boundless ambition of the Unicorn Clan Khan, Moto Chagatai, led him on a winter campaign across the Lion provinces. Although Chagatai’s campaign to capture the Imperial City was ultimately unsuccessful, the punishment he inflicted on the Lion forever changed the way the Empire regarded winter warfare. Few attempted to recreate the extent of that campaign, but most recognized it was possible to fight in the winter with adequate preparation and training. One group of ronin who served in Chagatai’s forces and survived the Lion’s vengeance went on to sell their services as couriers, messengers, and general supplemental cavalry, all with a specialty in winter tactics. The Yasuki family of the Crab would be envious of the discreet promotion the Snow Riders have conducted on behalf of their organization, and they have ensured they are always employed during the winter - if nothing else because their employers don’t want their enemies employing the Riders instead. Generally speaking, the Riders make adequate profits during the winter months to support them through the summer, which is exactly their intention.
Generalization: Although the story of this group is tied specifically to the Khan’s infamous campaign, there is no reason a small group could not develop along these lines independently of that incident. Doing so might make their services more difficult to market and sell, however.