The Baldr series is one of my favorite game franchises. Sky dive X is the fandisk for Sky(dive 1 and 2). It contains multiple stories. One is a complete new world with a new character who'll change the whole at it's very beginning. One is the story of how Rain and Kou met after gray xmas and their journey becoming mercenaries and hunting for their targets. There's also just random after stories or original random stories(a lot shorter than the 2 I already highlighted)
There's multiple game modes outside of the stories, such as hell challenge, survival, and an arena mode where the game randomly puts a set of enemies(from the weakest mobs to the final boss) against each other in 3 brackets and you can gamble on them.
Outside of the story mode you can unlock and play every enemy from the weakest mob to the final boss of the main game.
It's sad that Giga shutdown and the game can't be bought anymore.