How to get Harvey strongest weapon "Maid bringer " with a base attack of 750 what's the location of it can anybody pls tell me. And where can I find strongest weapon for Amelia?

How to get Harvey strongest weapon "Maid bringer " with a base attack of 750 what's the location of it can anybody pls tell me.

How to get marked in save files and what does it mean by newgame+ ,I'm new here so it's hard for me please can anybody tell me? and what about the progress in newgame+ is the progress become lost and how to open bonus content like it's showing in the marked files.