I'm putting this here, since this is the current game the Dev published and i couldn't find any other place where they're active aside from their itch io page. So...
Hmm... how to put this?
I like your characters (from Damien, Ciel, and even Zane -and Axel already looks interesting-). I've played this, the Main Game Demo and the other Short VN (the one with Ciel), and the Holiday Special as well. They're already unique in their own way, they're highly attractive, their Yandere sides are also differ from one to another, but.... there are a few things i want to point out to you.
(Please take this as a constructive and loving criticsm :) It's long, and of course, contain spoiler. And English is not my native language, so, expect grammar or speech error).
1. Their Personalities.
Instead of wholly laser-focusing on their infatuation with the MC for the whole game -whether in the main game or short stories-, i think it might be good if you also give the player some highlight into their personalities. It could make the player more engaged into the storyline even if it the short version ones, and could also make the characters more lively. What makes them, them?, What kind of a person they're out there?, How they genuinely interact with others?, etc. Even though i know the main game is about 'Yandere men taken interest in you', providing a glimpse of who they truly are as a person outside the infatuation would be great and appealing.
2. The CG.
I love the Damien CG in the main game ever since you changed it. But i personally dislike it when you didn't put anything in this one, and the other one (Apple for Teacher). I know both are simply short stories, but when you skip something crucial for a Visual Novel game, like CG, it leaves a bitter taste in the player's experience. CGs are crucial to emphasize equally crucial moments in Visual Novel, no matter if the plot is short or long -never forget this-. If you don't have the resource to or couldn't make a few of them, always try to, at least, make one. One CG is enough if you put them in good timing. And, just saying, hand-drawn is more preferable.
3. Pace/Length.
I noticed the pace, whether in the main game or in the short ones, is quite fast. Try to pace it more carefully so it doesn't resulting in short chapters (in the main game) or jarring execution (in short stories).
4. The Dynamic.
You're doing good with the dynamic between Ciel and MC -both in the main game and the side stories-, keep that up. But, with Damien... especially this one, feels a little bit uncomfortable. I don't know which or what part, but i feel like something about their Boss/Assistant dynamic is jarring to read. Not because his dark feelings for MC or something like that, no. It simply feels that way; Uncomfortable. Something is missing here.
5. The Warning(s).
You could add a little bit more specific warnings, since i saw a few players were quite upset with the content they got. For example, instead of listing only the major warnings that occurred throughout the game like Non-Con/Dub-Con, be more specific with it. In Ciel's route, for example, you can add 'Verbal Bullying', 'Verbal Degradation', 'Coercion', 'Mental Manipulation', and something else that represent his negative behavior to MC. And in Damien's route, you can add something more like 'Drug Use', 'Stalking', 'Controlling', etc and etc that represent his behavior/act to MC.
And.... yep. I think that's enough. Actually, i have a lot to say and have a few things i'd like to discuss with you, but.. since i don't know where to contact you where you active most, this will do for now.
Btw, overall, i enjoyed the main game and this one as well. I can't wait to see the main game complete! :).