I've been daydreaming all day about a game idea, where it's a tactical rpg where you have to advance through the game with the help of mercenaries, having to manage your money and objectives correctly so you can always afford their services every mission. Though of course I'm always thinking of the character dialogue and roleplaying elements, so each mercenary would be unique and have their own storylines that you can fulfill by renting their services enough and completing sidequests.
So "Fire Emblem, but they leave you if you can't pay them anymore"?
Yes, exactly actually! Though I imagine the game would have a core of cheap units, and the mercs being situationally free, such as during events that have personal significance to them, but in all the game would be about weighing your pocketbook against choices of strategy and trying to decide which mercs' growth to foster with your cash. I could also see there being a loan shark-type character, just so the player can't ever put themselves into a softlock and ruin their own run.
Though that gimmick isn't why I was daydreaming about it, more I was thinking about a videogame setting where all the characters are justifiably unscrupulous assholes, pulled together to a common cause through the siren song of needing a paycheck at the end of the day. In Fire Emblem, your units generally think you're awesome and are totally loyal to you and are 100% behind your cause from beginning to end; especially in Fates, where every character kisses your ass SO MUCH it's saccharinely sickening! I'd be more interested in a roster of characters that are generally indifferent for the cause you're fighting for, in fact they may low-key think you're a tool or an idiot, but they have needs and their own lives that need attending to and if you're the one that is helping them pursue their own desires, they'll play ball. And if you're not a good employer, it'd be a game mechanic where they'll lend their services to the enemy side, but of course they hope you realize it's nothing personal, and at the beginning of the next battle they'll be right there at your hub with their hand out.
So the real draw of the game is not the game mechanics, but the narrative where over the course of the game, you get to learn the minutiae of these characters' lives, come to know their personalities, get to enjoy watching them banter and rib eachother while on and off the battlefield, and help them grow and achieve their own goals.