Full disclosure: I reached out to Newman, one of the devs behind Ben X Slave Quest for any comment or interview, and have not heard back. That might be my answer.
I came across this game purely by chance, and was immediately sucked in. It's an erotic game, so there's parts of that in there, but there's a decent turn-based combat game, multiple choices that affect parts of the plot, and a decent shop system. This is all wrapped in a current alpha build of the game, so this is very promising. That alpha, by the way, can be found HERE. An APK version can be found HERE. Both are free to download and play, no Patreon support required.
The art is also quite good as well. It's a servicable porn parody of Ben 10 Omniverse. It's like, they could have nailed the original art, but didn't and moved it towards porn, which I liked. Now, I'm no fan of Omniverse, preferring the style of the original series, then Alien Force. Still, Newman and Akanoes made it work.
The story is pretty interesting: Albedo gets trapped in Alien X form and gets annoyed. Serena and Bellicus let it slip that the multiverse is going to be destroyed, and seem fine with it. Albedo convinces them to let him prevent that, by swapping him with Ben. Albedo takes control of Ben and plans to save the multiverse. While he works on that, Rook Shar is assigned to be "Ben's" new partner. He decides to make a minion of her, and then some. This is apparently encouraged by Max and Kevin, giving subtle hints to "Ben". An example of some out-of-character elements that seem right at home in this game.
The alpha focuses mainly on Rook Shar and attempts to corrupt her into a slave. There is one or two shots of Gwen, but as this is an alpha, not much can be done. There is one scene with Charmcaster too, but again, alpha. The art, as said, is pretty great. The girls look curvy in all the right places, and the outfits that Shar can be dressed in are nice too. She'll wear whatever "Ben" decides in and out of the house, but these changes don't seem to be reflected in battle. Hopefully that changes in future versions.
The battle system is actually quite interesting. It's turn-based, and turns are determined based on a speed stat. At the bottom of a screen, character icons move along a bar, with a turn given when the icon reaches the end. Currently, Shar can only cast a net that does minor damage and skips a target's turn. She can also use a med kit to heal damage. Albedo/Ben can turn into an alien and use a move, though the alien form sticks around for one turn. Currently, this is the only normal way to earn money to buy things. Some details suggest being able to make money using spy cams on Shar to stream stuff online.
The shops in the game have interesting stuff. Clothes for Shar, battle items, gift items for Shar, and two items that unlocked aliens for Albedo/Ben. It's limited right now, but again, alpha. There's all the indications that the shops will be expanded in future builds.
The girls that can be put to work for "Ben" seem to include Shar, different versions of Gwen, and Charmcaster, the top tier girls of Ben 10. No idea if any other girls will be included, but that's a fine number as is. I did see a promo image of Kai Green though. If they want to go extra, Drew Saturday of The Secret Saturdays really seemed to fight during the episode "The Most Dangerous Game Show".
Corruption is the name of the game here. The right combination of dialogue choices and gifts can get these girls out of their clothes and in "Ben's" good graces.
This is a pretty deep hentai RPG and deserves a good look, whether or not you're a Ben 10 fan. I put in a good few hours in just the alpha. Careful readers will see that the alpha was put up in Dec. 2018, and it seems like there was a hiatus there, but Newman made a couple of posts in recent days, so there's hope.
P.S. Albedo/Ben keeps referring to the Omnitrix as the Ultimatrix. There is an Ultimatrix in Omniverse, but it's used by Albedo to stabilize his natural transformations.