The spacecraft model is too delicate to be checked baggage, or placed in the overhead bins.
An extra seat had therefore been purchased. Hayabusa2 would sit beside me, and take the chicken for dinner.
Or... neither of us would fly.
It transpired the extra ticket should have been purchased as a "cabin bag ticket", not as a "human-be-flying ticket".
Now you'd think as the latter is more expensive, and the seat clearly reserved in my name, this wouldn't be a big deal.
OH SO WRONG.