¨Alone¨ is not exactly an easy theme… I´ll spend the first hour or two thinking up the game… maybe washing the dishes and thinking while I do this.
A quick idea that I had was some sort of shooter or dungeon crawler, where your ¨hitpoints¨ and ¨abilities¨ are defined by the companions that you grab along the way.
When your group is large, you have more options to act, and you can survive more dangerous stuff.
But if you have many people with you, maybe you can´t fit through certain openings in the game area, or you are an easier target…
I´ll keep thinking for a while.