You really need to fix the writing, which is likely why the comic itself struggled. A "vampire" that feeds on sexual fluids - that's a fucking succubus, you even gave her the mark. So just call a spade a spade. Now, her being a traditional "tease" just doesn't work. That would be like taking a fat kid that's addicted to crack, putting him in a cell at a buffet, sprinkling crack all over the food and forcing him to watch everyone else consume everything. I'd suggest checking out Zero End. She does really well sticking to the lore of such "monsters" and she has a "possessed" succubus character in her story, similar to Tsuki. She just went for the split personality rather than blending them into one singular entity.
You could do a Moxxie from the Borderlands games with Tsuki - a character who twists everything into sexual innuendo. That would fit, it would be a tease, but Tsuki is a character who would need sex and due to that need it would become an inherent addiction for that character. Your characters NEED to be grounded in what they are, or you risk just creating more generic schlock. Your concept is too strong to let it fall to that, so don't.
This is written like it was created by someone who thought there was actual value in their gender studios and psychology classes, yet failed to see the inherent double standards. We're literally dealing with trolly problems from Sasa or you get femsplained by Tsuki. Ever wanted to be told that your desire to stop a man from beating and raping his wives would just make you a wife beating rapist? This is the game for you! This rationalize comes from an absolutist ideology, either religious or third wave feminism which is just as dogmatic. Know your audience, don't preach to them.
She could, and certainly SHOULD question the MC's desire to be something more rather than just to replace the captain. Yet she states he will be a reskinned version of the same monster as if it were an absolute fact. It comes from a place that ignores that empathy exists. That people don't have to suffer to realize an act is wrong, or even to be told that an act is wrong to perceive it as such. It comes off as if it were being written by an overly educated idiot that fails to realize that humans, even in their most vile acts, are inherently logical creatures. We might do some incredibly illogical, monstrous shit, but you can ALWAYS trace the persons rationalization. For example, that's why Ted Kaczynski has actually developed a cult following decades after all the bs he did. It's why Charles Manson developed a MASSIVE following. Even the guy that killed the drug company CEO. Even guys like John Wayne Gacy, we find it disgusting, but we fully understand the rationality that led to those actions. And in many cases, people will agree with the justification, just not the act itself.
The premise that if you agree with the rationality, you will inherently become that same monster, is just inherently flawed from the jump. With "Uncle Ted" there are hundreds of millions of people who agree with his ideas, but they're not out there bombing airlines or colleges. They might do stupid shit like chain themselves to streets or something, actually making the problem they're fighting against worse through their actions, but most never even go to that extreme. Let alone go full terrorist.
Tsuki - I would definitely just straight out make her possessed by a succubus. Give her the personality where she twists everything into sexual innuendo so she can keep that teasing aspect to her character, but she's still going to be wanting to pogo on the MC non-stop. As it is, the "I want to tease right up to the moment and then blueball the MC despite the fact that i literally need his dick to live" just doesn't work. Yes, she is the only of your girls you can do something with atm, but the behavior just doesn't work for the character. It's self-defeating.
Sasa - She either needs to be the selfish princess or she needs to be the altruistic character she portends to be. She can have moments of the other, but she's going to be completely unlikeable if she continues to be morally inconsistent.
Hikari - We don't have enough yet for me to see her character as anything more than existing to be corrupted. That's... fine. To pull that off, though, she's going to have to be the focus of the game and she's the character we have the least amount of content for atm.
I'm not going to read your comics. You have to assume none of us will. This might have started as what you've stated, but you do have a strong premise here. It needs to evolve beyond what it currently is, though. That apparently is going to mean creating a branch off of what your story originally was. Basically spinning this into a completely separate reality.
