
Well, were to start to explain what's going on.
-The game is composed of four fronts, Leazas, Zeth, Helman and the free cities alliance, all of them got blitzed by Kayblis, who took advantage of the desert (yes, the same desert you use in Kichikuou Rance to blitz Helman and Zeth) Lia, Magic, Sheila and Copadon were unable to do anything beyond bickering, so Rance took the chance to claim command of the war effort, thus becoming the current leader of humanity.
-So far looks like JAPAN isn't directly invaded and simply sends their soldiers to support Leazas and the free cities, Agireda is the lowest commander supporting Leazas.
-Rance can support one front each turn, doing dark lord hunts and send military support. both options serve to reduce the damage the supported front receives and hunting the enemy commanders (both monsters and Dark lords)
-Silky and Hawzel work for Kayblis, most likely blackmailed in exchange for Hornet's safety.
-There is a good chance the current hero will have a role to do, since the game tracks how many humans got killed by percentage (at 10% escude can be used, at 30% it pierces the invincibility field, at 50% the hero is stronger than the demon king, at 70% with all dark lords dead he can harm gods)
-There are confirmed defeat scenes, at the very least for the Custom girls and Magic, no word if the defeat of a front means game over or the game continues. It has been suggested that the ending can vary depending how you fight, though.
-Every turn you can use meal tickets to get scenes with some of your characters
-The group is composed of the leaders (the ones you control in battle) with all the other recruited characters adding to the stats, so technically everyone is fighting.
-The war started before Rance got wind of what was going on, so by the time he takes charge of the human realm, Helman got trashed badly, the screencaps show Helman with more than half of their soldiers already killed.
-Kesselring and Babolat command the Helman invasion
-Medusa and Galtia command the Zeth invasion
-In leazas, apparently the one in command isn't Silky, Hawzel or Lexington, but the monster general Joseph.
-Pi-R and Lei command the free cities invasion.
The rest haven't been shown yet, so either they support the invasion in Zeth or the free cities, remain in the monster realm, or have gone solo (Seizel is suspect of this)