Dark Souls and Armored Core? That's a tough ask.
The pilot of a rusted mech wanders around a heavily-irradiated city in the hopes of finding a cure for radiation sickness that is slowly killing the human race, metts a few survivors along the way in their own mechs, finds frame parts, inner parts and weapons every so often to upgrade, there are a few mechanics alive that'll polish you and improve your weapons with research notes you gather from defunct facilities, and your main enemy is security systems of abndoned research facilities and experimental mechs. Then at the end when you beat Nineball, the mech that was first sent to retrive the cure, you either...I don't know. This is silly. And the Darkwraiths are a covenant that gathers all the radiation shielding for themselves. You invade other people's worlds through dimensional warping and have a good ol' 3rd person mech fight. You can hire mercenaries through terminals installed at the entrance to facilities and they will be airlifted in. Your currency is ball bearings and you get these whenever you destroy an enemy mech, and if you die, you have to find your destroyed shell to regain your ball bearings.