wow, this was so cute and charming (at least as much as a cosmic horror can be xd)! really love the character art, the designs look really stylish and nice along with the fact that their idle expression changes adds that nice bit of flare to what could have been just a static visual novel, well done! love the set pieces and background art too, a lot of them have nice varying perspectives with very cool framing, looks pretty nice! also love the monster designs, both cute and threatening at the same time (also love the among us bone corpse in the library xd).
the story has a good bit of intrigue too, very cool mystery! you have the general intro that lays out both the tone of the story and the personality of cosmo pretty nicely. then as you enter the realm, you learn alongside cosmo the nature of this world their in while building your frame of reference towards what is regular in their own world (like theres magic and visions, etc.). theres a double layer of world-building to create a general understanding of the story which i like! there were a lot of instances where you either introduced a lot of terms/characters or laid a lot question-leading tidbits regarding aspects of the characters or the world (like what happened with cosmo in the past, what is his relationship with his brother exactly, etc.) that will probably get explained later to allow them to act as narrative hooks to intrigue the reader later on with a payoff, but for an introductory chapter i think it would have been nice if some of those questions got answer by the end of this chapter, especially on cosmo's end. we get to know the personality of cosmo in this chapter, but we spend most of the time reading what he does rather than why he does it if that makes sense? having a slight look into his motivations and his insight for the action he takes (or you choose), even if they are just vague hints towards his guilt for his past (at least from what i can tell), i think it would allow for more investment in the character rather than cosmo functioning as just a vehicle to drive the mystery.
overall, this was a fun read to go through, love the world that you've created so far! also love the campy banter that cosmo and ji-hu go through during their time together, it was very fun to read! saw that you were starting the second chapter, i'm curious to see where it goes! great work!