Unity is my first engine, so is hard to me learn. Anyway, This game is going to be similiar to Monster Hunter. You are in a base, training with a simulator about killing Titans. The equipment you have is really easy. A sword, a bow, and 2 propulsors, one in each leg. In this way you can jump to the top of the buildings.
In the base you can choose Missions that randomly will choose an scenario and an enemy. The multiplayer is based in two game modes. PvP, that is a death mach with 3 colosal Titans walking in the scenario. And Wave mode, that is basically playing in waves of Titans in teams of 2, the best killing, the winner.
If you have any question, don't hesitate to ask, and any new idea is wellcome ^^ Thanks and