So I was right, the middle girl was hiding her size and was indeed having a pleasure rush once Cyan started growing massive. Now the question is, how big Cyan is gonna grow after she beats her and activate 3rd mark? Will she loose control after growing even more or since the King is not here, Cyan will time to prepare and test her 3rd mark growth? Then rescuing Kana arc begins.
I think human futanari are just the natural enemy of Maratians. Every time a human gets pumped full of Maratian sperm they evolve into an even bigger monster. Ironically if the Maratians just wore condoms they'd probably have won by now....