Have you considered switching to blinds?
Bill. —LH
When I suggest bribery, you don’t say a word, but when I suggest switching to blinds, you do. I see how it is. —Bill
On a serious note, anonymous, consider giving both your mimikyu and your pikachu something more interesting to engage them. Specifically, mimikyu sometimes enjoy scratching posts, as this allows them to hone their claws while indulging in their more imp-like tendencies. Your pikachu may switch to this as well if you can get your mimikyu to prefer this to the curtains. Alternatively, old rags or even bubble wrap and old cardboard boxes can be effective distractions, although be sure to keep watch and avoid letting your pikachu chew on the bubble wrap.
Either way, I also highly recommend considering blinds as opposed to curtains.