A very interesting concept indeed. I've played through the demo, and here are my thoughts:
-Your plot is consistent with what the Hololive girls have to offer. I really get the vibes of 'holo no graffiti' in there, and I have full confidence that when you start extending the plot, it will be just as beautiful. Albeit, there were some notable grammatical errors, I do believe it will be fixed for the final and stable version of the game.
-The art is splendid. I do not know if others can relate with me, but this somehow gives me nostalgia of when I played similar pixelated games, and that feeling is such a wonder to experience again, and the art truly does capture that moment. All the memes about each girl has so far been seen in combat, and it greatly adds to their personalities. As for the music, what I can suggest is that you add more variety of music for different situations, like one for introduction, for dialogue (and even then, add more variety depending on the present emotion), for combat, etc.
-The combat skills of each character are very diverse, and you can really see that difference when applying them on the combat field. This makes one want to actually come up with a strategy for when the combat skills extend. Although I have seen that, in my opinion, there are/is some character/s that are OP, but I believe that it will be balanced once the game develops more.
Overall, off to a great start, props to the entire team for making it this far already. As one meme says, "We will watch your career with great interest". Keep up the good work!