Isa could definitely be serious, but that was why he needed something like a birthday party...he needed everything they could get to lighten him up some. Although Sora's motives for this were perhaps a bit deeper than Pinkie's wanting to give everyone a party.

Sora thought for a little bit. "Although...how're we going to get him down here?" Knowing Isa, he'd probably be suspicious of any mysterious invitations to the cafeteria...but probably because Isa was suspicious of a lot of things.