Yeah, of course, always happy when my unsolicited essays disguised as itch comments end up being helpful! To follow up on a couple points:
Sparrow vs. Lilith, Round 2:
"[Lilith] and Shamy are probably my favorites to write" - this is telling, understandable, and I think you may be surprised as to how often this happens. By that I mean Lilith and Shamy being your favorites to write and not Daren and Sparrow. I'm sure there's a name for the phenomenon that I'm not aware of, but often you run into a situation where the primary protagonists are so intertwined with the central plot that the side characters are allowed to breathe more and become more interesting.
I think part of the issue here as well is that we don't learn much about Sparrow as a person other than "asocial" and "pretty" until the very end of the demo, and some of her dynamic with Daren might shine through more clearly in the second act now that more of her character is on the table. This is also especially true if a reader doesn't press the conversation in the library and doesn't help her walk home after the lab. If Darren x Sparrow is a lock, I'm not sure some of these actions can be optional unless they lead to bad endings since there are, to this point, not enough meaningful interactions between the pair to realistically get to the current state if you lose one.
What I would focus on going forward is: what about Daren and Sparrow excites you? You decided to write a whole book about them, so what is it about them that makes you really interested in telling their story? The more you can show this dynamic in each of these characters, the more compelling they'll be, and maybe you'll get some of those people jumping ships from Lilith to Sparrow soon.
On the Matter of End:
No no no don't cut End, that's not what I was saying. I think having him in there is fine, every good band needs a guy who makes the sandwiches. My point was just more of a matter of balance - End has approximately as many meaningful interactions with Daren in the first act as Sparrow does, and if one of the main like two purposes of the story is for Daren to get his snuggle on with Sparrow that might be sub-optimal.
If by Lilith's condition you mean her being spread too thin, I think that absolutely could have been delivered by Tower, just in a way that's less emotional and empathetic and more, like, academic. Something like "Mm. I have noticed that since the beginning of Lilith's assignment with [fennec whose name I can't remember] she has become 14% less productive in her other tasks. I am concerned that we may need to reevaluate our resource allocation." Like, you can show that he notices and cares in his own way.
I think going forward maybe trying to replace some of End's appearances with Tower is a good idea. Based on what you said in your reply, I wonder if you're putting End into too many scenes to kind of justify his existence, and I think you can afford to have him take a backseat more often.
Other things:
Forgot to mention this before, but minor gripe: when Tower's sprite is mirrored it switches what arm is mechanical. I am not a visual artist and I don't know how easy that is to fix.
I'm always happy to be a sounding board for story and character ideas, but to reiterate I still think you've got a really solid foundation here :)