For Kaisai's signature spell, do you choose targets when casting the spell or when it resolves?

Ruling: You choose the target when you play the spell and it goes on the chain, not when it resolves.

Nuances:

• This means you must commit to targets before your opponent can respond, potentially requiring you to overkill a unit if you anticipate a buff in response
• You cannot wait to see if your opponent responds before allocating damage to multiple units