I bet it's a joke on how onigiri has become an upgradable item recently. Akashi is right there.
So, because Kasumi is asking for seconds (in the artist commentary), they put on the masks to make more. It's a serious process, I guess, same as upgrading heavy machinery.
OR, she already ate the upgraded onigiri, and she sparkles so much that they have to put on the masks to shield their eyes.