How can I make the main character and the battle party separate?

So, I can't figure out what I need to do in order to make a feature I want.

The main protagonist(lead character/main character) on the map needs to be separate from the actual party members(battle party). Which means, the protagonist should NOT be shown in the character selecting screen, menu, battle, etc., and the battle protagonists should NOT be shown as a lead character(should not be shown on the map), etc.

I've tried to search up this topic with a bunch of different keywords, but the feature I want didn't showed up.

Can someone please help me on what plugins I need to download, or which java script file I need to modify in order to accomplish this?

RPG maker MZ by the way.

Thank you.