Does Yasuo's legend ability start a chain, and can you react to it to kill the chosen unit before it returns to base?

Ruling: Yes, Yasuo's legend ability goes onto the chain when it triggers, so you can react to it with something to kill the chosen unit before it goes back to base.

Nuances:

• Not all abilities go on the chain; replacement abilities do not go on the chain, but Yasuo's ability does.