Target 1 face-up monster you control; it gains 200 ATK/DEF for each card your opponent currently has in their hand, until the end of this turn.
Rulings
Individual Card FAQs
When "Hayabusa Knight", boosted by "Energy Drain", attacks, and the opponent's hand is reduced during the battle, the ATK of "Hayabusa Knight" for the second attack is not changed because the effect of "Energy Drain" is determined when "Energy Drain" resolves.
Trap|
Normal