I just finished playing and!! This was very cute and fun!! I especially enjoyed the section in the demo where you need to deduce who (insert spoiler here). Compared to Locked Room on Rails, I will say that the art and general game direction have improved quite a ton!! I can tell how much effort you put into each background piece, and that effort just made the game more engaging. Although there is a setup for multiple characters and their relationships with Desirée, I found my attention the most engaged when she was interacting with Irina. I really like the Detective too, as well as Maximillian (his interactions with the Detective add some fun comedic value since it's satisfying to see him get shut up).
I think my only major criticism I have (it floated in my head a lot while I was playing) was that some scenes felt like they were missing music? It could definitely just be a stylistic choice, but one example that comes to mind is when Desirée first bumps into Irina. Her introduction on stage was very nice with the accompanying music of the ballet, and the glamorous visual of her up close, so I thought Desirée actually meeting her face-to-face would carry that same sort of wonder and enchantment! However, the lack of music just made it feel awkward and not really anything else. The times there were music, I loved it!! I wanted to hear more, especially for such an important character (I assume). I'd love if Irina had a theme that accompanied her to contrast with Forget Me Not's upbeat, jazzy, playful melodies.
Overall, this is an effective (and very endearing) demo!!! I can't wait to see more from you!!