This card can clear your opponent's field very easily, by not destroying cards like "Call of the Haunted" or Equip Spell Cards, or even by removing your own "Koa'ki Meiru" from the field before it resolves.
Keep in mind that this card activates its effect by your opponent having more Monsters than you do, BUT you destroy cards (not just monsters) controlled by your opponent until it equals the number of monsters you control.
ie. You have 1 "Koa'ki Meiru" monster. Your opponent has 5 monsters and 6 Spell/Traps on the field. You can destroy your opponent's cards until there is only one on their field.
If that one monster is "Koa'ki Meiru Maximus", you can use its effect to destroy the last card, clearing your opponent's field completely.
Summon another monster(s) during the turn you use this effect to overwhelm as much as possible.
If you chain a card like Compulsory Evacuation Device to this card's effect to return your only "Koa'ki Meiru" monster to your hand, you can destroy all cards your opponent controls. You can then summon that monster back to the field for a direct attack on your opponent's Life Points.