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Basically? Do as you like. You feel like this needs to be explained? Okay, explain. If not? Then don't.
Do it for the important characters (like the chaos gods, their girls (wives, and daughters), or the currently being used as a way of exposition/information carrier, etc), but don't for the cannon fodder/everyone. Because we don't need to know how the chaos gods were ripping and tearing a whole bunch of lesser demons; you could just say that they were ripping and tearing lesser demons. Because, even if hard, when you find that balance of giving just enough information; not too much that it's just an information dump, and not too little that it's just skipped over, then you hit gold.
It's either a trap, or we're going to see some graves (her parents).
DxD
Both can technically work. For a battle frenzy system, you need a good foundation/backing to supply you with soldiers, ammunitions, weapons, and so on. For a farming system, you need to defend your land; as well as get more land, to farm more.
You know how in Gacha they have the user gets lucky early on? Yeah, this was his guaranteed rare; he may get some more later on, but then he'll just have so many commons.
Well... at least you can't say, that their love life is boring.