Kai'Sa is a good choice against assassins for several reasons that exploit her survivability, repositioning, and consistent damage. Here are the main factors that make her strong in this type of matchup:

1. Mobility with Ultimate
Kai'Sa's ultimate, Killer Instinct (R), allows her to quickly reposition herself, out of reach of assassins trying to eliminate her. This ability is crucial to avoid direct engages from champions like Zed or Talon, who rely on immediate burst. In addition to Kai'sa's ''E'' making her invisible and always having a good positioning, in addition to the inability to dodge the key skills of assassin champions, such as Katarina's dagger, and also ''E'''s passive makes you have it several times in a fight, even without navori.

2. Plasma Passive and Sustained Damage
Kai'Sa's passive, Second Skin, applies stacks of Plasma, which increase her damage over prolonged exchanges. Since assassins generally have high burst but aren't as effective in long exchanges, Kai'Sa can punish them if they can't eliminate her quickly. In addition to other reasons that any Kai'sa player could say here.

An interesting fact about Kai'Sa is that she is the first League of Legends champion to interact directly with the Void without being completely consumed by it. Her story is unique because, when captured by the Void as a child, she survived by fusing with a symbiotic creature from the Void. This symbiosis gave her supernatural powers and her iconic biological armor, allowing her to fight the Void instead of being dominated by it.

This characteristic also makes Kai'Sa a complex figure in the game's lore, torn between her humanity and her connection to the Void. She is often called the "Daughter of the Void", but maintains her identity as a determined survivor rather than a servant of dark forces.