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I cannot speak to the developer's intentions. However, my best guess for why the Android port costs money is simply to age-gate it. 

I genuinely hope you folks are taking care of yourselves. I recall ages ago saying that the three porn games I was most excited for this year were Goblin Nest, Alien Invasyndrome, and Adult Escape from Zombie U. Welp, It's December and BadColor has pushed back the release for Goblin Nest because they need more time, Mozu Field hasn't released a December demo build yet because they're suffering from back pain.  Now, does this mean I desperately want a Adult Escape from Zombie U update more than ever since I don't have the other games? Hell no! A lot of developers have needed extra time lately, it's not just you guys. If you think your pie needs more time to bake, it needs more time. Take it easy this holiday season and take care of yourselves.

I've been checking these comments daily for news of an update for a while now. I'm just going to do the sane thing and give nidio a follow, instead. Honestly, between Adult Escape From Zombie U(nidio), Goblin Nest (BadColor), Alien Invasyndrome (mozu field), and Project Dungeon (HUuuUGe) I'm super excited for the hentai games that'll be released over the course of the next few months/years. Keep up the great work in the face of adversity, you H-game devs are most thoroughly appreciated.