When using Radiant Greninja, do you have to discard the Energy every turn you use it's Ability?

Question

Here's the card in question:

Answer 1

Yes, you have to.

"Concealed Cards:
You must discard an Energy card from your hand in order to use this Ability. Once during your turn, you may draw 2 cards."

The text only says that you have to if you use the ability, it just functions like any other "Discard" ability, but with a single energy.

Discarding is optional, but if you choose to do it a single energy must be sacrificed.