Is it possible to create a skill that performs an animation on the user and automatically kills the target if they are affected by a state  (in this case, if they are stunned)?

It would be something like this:
Player stuns the enemy >>> The vulnerable enemy can now be affected by the takedown skill >>> The player uses the skill, an animation plays  and the enemy dies instantly.

It would be something similar to the takedowns we see in some games like Far Cry or Watch Dogs, where the player can automatically kill vulnerable enemies.

Currently, in RPG Maker only has condition to check if player is inflicted by a state but not events. I'll add a condition for that in next update.