Forum:Ryu Kokki VS Diffusion Wave Motion

Player A has a Ryu Kokki face-up on the field.

Player B has a Dark Magician face-up on the field.

Player B activates Diffusion Wave Motion during their Main Phase 1.

Player B moves into their Battle Phase.

Player B attacks Ryu Kokki with Dark Magician.

My question is: Does Dark Magician get destroyed?

Diffusion Wave Motion says "The effects of Effect Monsters destroyed by this attack(s) are not activated."

Ryu Kokki says "If this card battles a Warrior or Spellcaster-Type monster, destroy that monster at the end of the Damage Step."

Does Ryu Kokki's effect activate during the battle step, and therefore Diffusion Wave Motion does not effect this...

Or does Diffusion Wave Motion cancel Ryu Kokki's effect because it is doing something after it has been destroyed...

The specific card rulings on this site of "Diffusion Wave Motion" give examples of cards that would be negated, but all of them start with:

"If this card is destroy and sent to the graveyard..." or "If this card is destroyed by battle and sent to the graveyard...".

Any Ideas?