Finish with different rankings to unlock new sets of starting weapons:

Easy, "A" rank: All handguns and shotgun.
Easy, "S" rank: All weapons (except charged particle rifle).
Normal, "A" rank: All weapons (except charged particle rifle).
Normal, "S" rank: All weapons with unlimited ammo(except charged particle rifle).
Hard, "A" rank: All weapons with unlimited ammo(except charged particle rifle).
Hard, "S" rank: All weapons with unlimited ammo.