This isn't really a "game" so much as a trailer for a game. You use an item, talk to some NPCs, view a scene, then it's over.
It also suffers from a severe case of "Why Should I Care?"
Like, I'm confused as to what the MC is supposed to be. At the end she mentions she was turned into a succubus, and that she's no longer a vampire...but previously a vampire was referred to as being separate from the queen? A previous poster was under the impression that she was a human turned into a succubus. And she does LOOK like a succubus.
We also don't know anything about Akira except: Has a boyfriend, has a mom, has two sisters, a servant, and disobeys her mom.
We don't know: Who is this boyfriend, what she actually IS (yes, it says she "was" a vampire but we need some worldbuilding to establish what that means), and why her mom is so impatient. Moreover, we need to know what "mom" actually means.
We learn more about Akira's SISTER than we do about the character we're ostensibly meant to be playing as: She's got two sisters, a mom, she's some kind of vampire-demon thing, she likes to snitch, she likes to fuck goblins or whatever, and the mom trusts her.
There's no meat here. You may as well just skip the entire sequence if the game is created since it can be summed up in a single sentence: "I'm stuck on Earth as a succubus because I went off to fuck my boyfriend when my mom sent me out on a mission." Cuz that's pretty much all that happened.
Advice for fixing these problems:
1) Take some time to explain what the MC, her sisters, and mom are.
2) Show us, don't tell us, why we should care about the MC and her boyfriend. Why is he worth disobeying her mother for?
3) The mother indicates this isn't the first time she's disobeyed. Show us or at least tell us what this means.
4) Gameplay! We have this HUD full of stuff but we don't know what any of it means. This sequence AKA demo should be about showing the player what gameplay will be like, not a glorified cutscene. Go look up "Verticle Slice" in terms of game design for what I mean here.
5) Trim the third sister (Yumi) out of the opening. Have a single line mentioning she's off doing something else. There's no actual explanation for why all three sisters were called in anyway. You can always introduce her later, and make it a surprise for the player. Also consider trimming Faye, since she doesn't do much. There's nothing stopping you from having the blonde sister wake up the MC and get irritated at her for staying in bed. If you have plans involving Faye, it'd be a good idea to show this.
6) If the three sisters are meant to be sisters, consider unifying their naming. Akira, Yumi, and Rachel sounds...off. I did some digging, and "Rachel" can mean "Sheep." If we want to match the other two, you could call her "Yoko," which can be written with the 羊 or "sheep" kanji.
7) Drop some books in the castle that give details about the setting. Who we're dealing with, why we're dealing with them, and what it all means. Remember that the common belief among most people is that vampires are turned humans and succubi are demons. In the hierarchy of fiendishness, they're either completely separate from one another or succubi are more powerful. This dynamic being flipped would thus need an explanation.