It is widely understood by historians of La Metal that Hoshino Tetsuro was not the first human boy taken to that world by Maetel. It is less well-known that he was also not the first Earthling, nor was he the first to reject mechanization.
Humanity had many false starts before developing interplanetary flight, including the creation of land trains before they ever escaped their own atmosphere – some of which had a curious resemblance to the 999.
Perhaps this was why a beautiful and mysterious traveler could coax a little Japanese boy on board a train to Andromeda a decade before Gagarin left Earth's atmosphere. Or perhaps, in the aftermath of such a devastating war, nearly any boy would have accepted; she merely selected the one who shared a name (or was it really just a nickname? If so, she didn't know) with her mother's cat.
He spent the long, long time on board with a sketchbook in hand, patiently drawing the sights of deep space and alien worlds, rarely venturing too far from the station. He was not eager to risk his life in gun battles. But his spirit burned with the passion of youth, with an ambition to create something amazing. The boy came to fear, after meeting mechanized humans, that obtaining all the time in the world would not let him fulfill his dreams. That all a mechanical body offered was the chance to truly procrastinate forever.
It is not known why Queen Promethium allowed this boy to leave Andromeda without a mechanical body. Perhaps, so early in both the free mechanization program and the Machine Empire's history, she had not yet decided on a policy of coercion, and feared bad publicity more than she did other children obtaining cold feet. Perhaps something about the boy impressed her and reminded her of the days when she had a beating heart.
Circumstantial evidence, however, suggests that the two cut a deal.
It should be noted that, not long after their encounter, La Metal gave the Comet Station Library, at the edge of Earth's system, where the boy had once checked out all the books he could carry, an extremely generous donation. That the boy grew up to draw manga for a living, and although the library indeed catalogs all books from Earth, the ones which he created always received the most prominent display. That, for all that the galaxy remembers her as a tyrant, the boy wrote at least one tale depicting Promethium as she was in her youth, and perhaps, for all her regrets, as she wished to be remembered: as a beautiful woman and a friend of humanity.
And that it is not clear where or indeed whether he was buried.
Perhaps Maetel came back for him in his old age, once his flesh and blood body was all but used up; perhaps the problem he foresaw was with early mechanization, not with mechanization entirely. Or perhaps he had to leave any body at all behind, and it is only his spirit which came to sail the sea of stars, en route to La Metal.
So long, Captain!