Sure we got small bits of info and lore like from outbreak perfected, but after Rise of Iron it feels like SIVA was just completely forgotten and never mentioned in depth again. I’ve heard people call RoI a filler dlc because it was just kinda brushed under the rug and Aksis as well as the entire storyline of SIVA was just never used/mentioned again. It’s a real shame considering how unique SIVA was as well as the potential it had for further story usage.
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It was a one-off. SIVA was never meant to be a reoccurring foe, it was created for Rise of Iron and only Rise of Iron and after that the story was done. "Wrapped up nicely with a little bow" as Luke Smith would say.