The Discovery
During their trip in the Burning Sands, the Ki-Rin Clan came across a fabled animal known as the Unicorn and its smaller cousin, what they call today, the Warhorse or Utaku Steed.
Why is it special?
The Utaku Steed have one less pair of ribs then your normal Rokugani horse. It is slightly shorter then the common riding horse but considerably leaner and more muscular. Centuries of living on the sand made it fleet of foot and have an almost supernatural equilibrium that it passes along to its rider now that it is domesticated. The desert's hot air also game it larger and more efficient lungs that allow it to run great distance with unmatched endurance. All these genetic quirks come with a price though, a fater metabolism. These steeds requiere more food and water then normal horses. They have a lifespan of 25 to 30 years. The Unicorn make them retire of "active duty" at 15 for breeding purposes.
Utaku Steed today
Now these horses are bred only for the Emperor, the Unicorn Clan and Family Daimyos and for the Battle Maiden who ride them into combat.
References
L5R Way of the Unicorn p.99-100