Hi there! Thanks for giving the game a try!
Braver is built to follow classic JRPG design, much like older Final Fantasy titles, and uses that traditional 4-person party structure.
That said, it is *technically* possible to run solo all the way to the end of chapter one (there’s even an achievement for beating the first chapter that way), and that's probably what you heard about.
But this requires a high level of system mastery and isn’t intended for a first playthrough. And anything past chapter one simply isn't possible, nor very fun. The full game isn’t designed to be completed entirely solo.
If you decide to try it again with a full party, I think you’ll have a much smoother experience.