I agree with the above comments.
At first I thought that the events of this game might have occurred before the ship was taken over by the captain from the main game. However, this is impossible given that Shuma is already on the ship with the rest of the crew.
Given the title, this is an alternative universe where the original main character never became captain, Mia got her hands on a bunch of small aliens that eventually broke free of their confinement and had sex with the girls on the ship.
There’s not really much context to it other than that. In order for this side project to make sense, Nergal should add a final scene, or at least a dialogue, showing where the crew ended up. Given what happens in the game, they’re probably in a cave ,somewhere, being bred non-stop. However, considering who the developer is, we might not get even that. This is simply a side project meant to buy time while Nergal hopefully deals with his other games.
It’s not really an NTR since the captain doesn’t exist, hence he’s had no relationship with the girls. The only cheating here is that Kittana is once again having sex behind her awful husband’s back, which she already does in the main game with the MC.
Regardless, I see why this might be perceived as an NTR from the player’s perspective. These are supposed to be counterparts to the women that we spent time getting close to in the original game; years considering how long its development is taking. Therefore it still feels like cheating to us, even though our character isn’t and has never been there with them in this version.
I agree that adding scenes like these as part of the original game would make more sense, given the right context. But Solarion’s main storyline has remained stagnant for a very long time in favour of short updates featuring new sex scenes.
Plus, and I say this as someone who enjoys NTR games when done properly, developers need to be clear with their audience. Some people simply dislike certain contents. Therefore, if developers wish to make a sex game featuring both vanilla and NTR scenes they need to specify it from the beginning in order to gain the support of the kind of audience who enjoys these games.
On the other hand, if you advertise your game as simply containing vanilla, but add NTR scenes after a while, you’ll inevitably lose the support of part your audience. Specifically the ones who were only financing you for the vanilla story.