Irelia's ultimate tool tip isn't accurate?
Irelia launches a storm of blades that explode outward upon hitting a champion. The blades deal 125/225/325 (+70% Ability Power) magic damage and Mark champions and large monsters for 6 seconds.Irelia then forms the blades into a wall for 2.5/3/3.5 seconds. Passing through the wall deals 75/125/175 (+70% Ability Power) magic damage, slows by 60% and disarms for 1.5 seconds.Disarmed enemies cannot basic attack.
It does not say that the first champion hit will also be slowed.