I'm certain the platinum requires 2 playthroughs on normal and 2 on hard, no? I've already done the full hard mode once and am going through it again starting on the opposite side. I'd save the killer weapon and rampage for the 2 normal runs.
It'd lead you to believe that in their descriptions, but you can actually obtain it through just two playthroughs.
You just need one White and one Black playthrough, and also one Normal and one Hard, to unlock both Red Sides and both difficulty levels in Stage Select. (Ex: A Normal Black and a Hard White)
Then you can just play the Red Side of the side on each respective difficulty that you don't have the completion for, and it'll register as a full playthrough for the trophies.(So for the following example, you'd have to do Normal White Red Side and Hard Black in Stage Select)
So the pack can be completed in just 2 playthroughs if you're smart about it, and some grinding in Free Mode for some of the item based ones.
Easiest pack yet from Platinum.
I'm glad it works that way though, 4 different playthroughs would be a little much for this game's single player, considering nothing really changes besides the Red Side
Edit: You also have to make sure you do the Max fights you missed as well in stage 4. As long as the game sees a ranking for all main acts after the credits it'll give you credit