Pokemon.This one is mostly Wicke from Pokemon in Rule 34
Click on this Splatoon Tag to display all Splatoon posts. Theres a couple posts of Splatoon futanari in the tag. In the first ones. Not much for Marina though.
Marina the dark skinned octoling from Splatoon 2 seems to be popular so heres all the best Rule 34 i could find in a quick look.