The Soldier hasn't yet achieved a high enough level in friendship to get the full story, but Sento says, "Back on my world, there was an organization called Faust. They were doing some...rather untoward experiments with Nebula Gas, a substance derived from a Martian artifact. I tried to stop them. That first attempt did...not go according to plan." There's a pause. "Among other things, prolonged exposure to Nebula Gas can cause severe memory loss."