Across JRPGs of all subgenres, whether high fantasy epics or urban fantasy adventures, the party is what defines how memorable the central cast of characters is. If players don't feel attached to the people or creatures they're utilizing in battle, then there won't be any connection or spark in the story, and things will fall very flat, very fast. Leveling up these characters is the core component of many games, where part of the appeal is discovering what skills they have available to utilize.