The amount of variables this game tracks is a bit excessive. I wouldn't be surprised if half of the audience completely missed Ellie's content purely due to the fact that certain items are required to trigger certain scenes. I'll leave a rough list of what to look out for (I might edit this later to create a proper guide):
The key mechanic behind this VN seems to be building trust with Ellie, which will open the doors for corrupting her later on (essentially leading to lewd scenes).
Ironically, you can completely miss ALL of the content from the first release of you don't get the required amount of trust with Ellie. This is the first time I've seen a dev heavily punish their audience by outright removing any semblance of a plot while obfuscating the "correct" path.
*Edit: The "Key Choices" spoiler has been renamed to "Choice Guide", and all choices have been included broken down into each day.