Kai'Sa ADC vs Yuumi Support Matchup

Why Kai'Sa is favored

Kai'Sa excels into Yuumi lanes because Yuumi's attached state leaves only a single enemy target in lane, allowing Kai'Sa's Icathian Rain(Q) to concentrate its full isolated missile burst without splitting between two champions. Furthermore, Yuumi provides no pre-6 hard crowd control to peel aggressive all-ins, enabling Kai'Sa and engage supports to burst down the host and immediately kill the detached cat.

Measured in High Elo: Kai'Sa wins 2.4pp more often than expected over 4,248 games.

How to play as Kai'Sa

When Yuumi is attached, focus the host; thin the nearby wave before using Icathian Rain(Q) to send more missiles into that champion. (Unverified: no source confirms this note.)

When Yuumi detaches after her host dies, attack her if she is in range and the fight is safe; watch for her to attach to another nearby ally. (Unverified: no source confirms this note.)

Use Killer Instinct(R) only on a visible, Plasma-marked enemy within your rank's range, and choose a landing point where you can avoid the enemy team's follow-up.

While Yuumi is attached to an ally, she is untargetable and cannot absorb hits, ensuring Icathian Rain(Q) concentrates its entire missile volley onto the host ADC once minions are cleared.

When her attached ally dies, Yuumi is detached at their location and becomes targetable; she can still attach to another nearby ally if one is available.

How to play as Yuumi

When Kai'Sa or her support can land immobilizing crowd control, stay attached; being hit while detached locks You and Me!(W) for 5 seconds.

Yuumi has no hard crowd control prior to unlocking Final Chapter(R) at level 6, offering only minor slows and shield buffs to protect her carry from high-burst all-ins.

Sources

These notes come from LoL Wiki and r/kaisamains, checked against the champions' abilities.