Seth

Sorry if these are wrong info lol

He knows about lost technology and how to fix, repair, and possibly even create them (if he has enough materials), he learned about it back then cause he was pretty interested about how they work.

BUT, he keeps it secret lmao, and only works with the "modern" stuff they have now.

If they ever meet, I think he can even perform maintenance stuff on Vash's arm.

Not good with lethal weapons and fighting so he sometimes would create mini drones/robots stuff. And would carry guns that only use rubber bullets instead, for intimidation lol, he also thought about making a taser gun at one point.