Ginga Tetsudou 999

In the future, mankind has been able to create machine bodies so they can be able to live for thousands of years.

Humans are now second class citizens and if they do not acquire an mechanical body,

they are either hunted or forced to live a life of poverty.
Tetsuro Hoshino is a young boy whose mother is killed by the machine men for a hunting trophy.

Outraged, Tetsuro seeks out revenge and vows to keep his word to his mother to get a machine body.

He soon meets a woman named Maetel who gives him a free ticket on the space train Galaxy Express,

which if he rides, he will be able to receive a free mechanical body. But nothing is as it seems as rumors rise that all who board the train never return.
This is a story of how one boy learns about the world and his quest for a new body.
Note: Originally serialized in Shuukan Shounen King from 1977 to 1981, a sequel was serialized in various incarnations of Big Comic from 1996 to 2005. In tankoubon form, this sequel wasn’t released as a stand alone titled, but tacked on reprints of the original series. This means, for example, that Shogakukan’s 1997 release covers the original series in volume 1 to 14 and the sequel in Volumes 15 to 21.
Won Shougakukan Award in 1977 for Shounen Manga category

Viz released five volumes of the sequel. The original manga has yet to be translated into English.