Can you react to VI's boosting ability after it's announced and paid for but before it resolves, and does each boost happen one at a time?

Ruling: Yes, you can react to VI's boosting ability after the cost is paid but before it resolves (for example, by bouncing VI back to hand with Gust). Each instance of the ability must be activated separately because it lacks the Reaction keyword.

Sequence:

• Player pays the cost (left of the colon) to activate the ability
• The ability goes on the chain
• Opponents can react before it resolves
• After the ability resolves and leaves the chain, the game returns to a neutral open state
• Only then can the ability be activated again

Nuances:

• The ability must be used one at a time; each boost can only occur after the previous one has left the chain and the game is in a neutral open state
• This one-at-a-time restriction applies because the ability lacks the Reaction keyword
• Even if a card had an Action keyword, it would still only be usable one at a time (Action just means it's useable in showdown, which VI's ability is not)