My main answer will sound like the girliest answer I can ever give, and I’m ok with that.
Romaance and friendship.
Yes, many RPGs have friendships as part of the storylines, but in most games, the closeness of the stories is prewritten. In this series, your gameplay dictates the relationship of your characters. If you play characters side-by-side their friendship grows. You view their budding friendships through conversations. In those conversations, you learn a little more about each character. Every conversation is unique.
The higher the friendship the more benefits you have in battle. A character with an A-level friendship may have an enemy act completely repelled by a close friend. Even if you don’t care about the relationship aspect this gives you a reason to make sure everyone is close to everyone.
Romance in the games is often regulated to otome, visual novels, and farming simulators. It’s rare to find action-based games with romance and marriage aspects to them.
Strategic RPGs and permadeath
This series made me realize that although I love open-world games, there is something about a board that appeals to me. Moving my units around in the most strategic way to outmaneuver my enemy is a rush. All with the knowledge that if a character dies, they’re gone forever. Yes, I restart consistently, because I don’t lose characters.
We all beat the game together, or no one does.