Reverse or Rebirth...?

Wow. I have no idea what you're talking about. XD

I mean, I know about Timeless weapons, but what are Reverse/Rebirth weapons?

This annoys me, not knowing. I read what I can about KMS, but I guess some things slip by me.

Reverse (or rebirth) weapons are the same as Timeless weapons, except they're 2 base attack weaker, much easier to get, and has 4 levels, whereas Timeless weapons have 6 levels and are only able to be forged by killing Pink Been and collecting 3 Time Stones and other materials.