Various cheats        

1 weapon mode:
     To get 1 weapon mode, you have to beat the game once in Brand New
Fear File with any ending in hard mode and get 10 Stars.

All Weapon Mode:
     Beat the game with any ending on hard with the 1 weapon mode.

Eileen's Sub-Machine Gun:
     To  unlock  Eileen's  Sub-machine  gun beat the game in hard in a
Brand  New  Fear File and get at least 9 stars. If done correctly: You
can get the Sub-machine gun in your first visit of the Apartment World
in room 102.

Chainsaw:
     Beat  the game once in any mode and Chainsaw will be available at
the Forest (First) in the area where there's a car.