Until end of turn, creatures you control get +2/+2 and gain "Whenever this creature deals combat damage to a player or planeswalker, destroy target artifact or enchantment defending player controls."
Storm the Citadel affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t get +2/+2 or gain the triggered ability.
2019-05-03 • wotc
If a creature is attacking a planeswalker, the controller of the planeswalker is the defending player.