By forget about you meant immediately roll out from under the kotatsu to go grab it, right? Right. Cuz that's what Kai was doing, immediately, right now.

"A Christmas cake!" He exclaimed, moving with Great Speed to grab that box. "I'm going to eat it."

Here, let him just scoot that whole cake that he absolutely put zero effort into whatsoever, definitely that was the only other cake around, definitely it was just Eh-- let him scoot that over fully in front of Kyoko so there was room for a whole second cake between himself and Shinji.