Uchû Kôkyôshi Maetel
~Ginga Tetsudô 999 Gaiden~
Episode 12 “Yûshi-tachi no "Wakare no Kyoku"”

Planet Prometheum, the stronghold that Tochirō tracked down, turns out to be a mechanized planet covered with self-regenerating mechanical cells.

There stands the queen who has achieved complete resurrection, and a mechanized being called Maetel.