If you had told me, a few chapters in, that we'd get this reveal, I would have assumed it was for Belka, or maybe Ken. But no matter, it had to be somebody.
The label “707” on the box is a reference to the manga “Submarine 707”, which is credited as the first submarine manga. It was a couple of years before “Blue Submarine No. 6”, and by the same author: Ozawa Satorou (小沢さとる).
And if you ask me, the spaceship that appears in one panel looks a lot like the one from “Life Force”.