Anime - set in space, family abducted by aliens, brainwashed into fighting for them against Earth. Except one who escapes and fights with Earth. Ends with one-on-one fight between a pilot in mech suit against the big bad alien boss

I watched this as a kid in the late 90s/ early 20s. It felt like a long running show. A family is abducted by aliens and all except one of the sons escape. But I think he's been worked on to be half mechanical. His family have been brainwashed and he has to fight them. It ends with our hero fighting the 'boss level' alien on the moon (i think).