Spoilers follow, etc etc.
Theme: The tower being very big and hard to navigate?
Story: Mutual unrequited love + curse.
I didn't love starting with the expositional world building. Some of it was pointing to things that sounded like they would be more interesting than revisiting this tower barring the handsome woof trapped in side.
Frankly, I'm not the biggest fan of the voice of more classical works, which I think you do like and carry forward with you. It felt out of place with the tale, as that felt like a more modern harlequin novel standby, as opposed to the buffoonery of something like Far From the Madding Crowd, or other works that were contemporary with it (what else could I call it other than such when one uses divination to send the most eligible bachelor in town a letter saying "marry me"?), and in that, it made the voice feel discordant with the narrative, for me.
Just because it's "fantasy" it doesn't have to be archaic/medieval in all conventions. You mentioned physics and in the same breath had people saying "Damnation".
I liked the attempt to take the curse onto the self, although I don't know if I feel very convinced that it should have fully abated with the mirror's shattering, given the difficulty in removing it from the (insert-name-here protagonist). It would have made more sense to me if the affliction was shared between the two, given it was an echo of the original, and in that, I think you could have progressed to a more satisfactory ending other than "I failed to do what I wanted due to external forces and not being brave enough and then selling away my desire to say so to abate my suffering".
It's also a bit nebulous why the curse kicks in there, given he's like "I can seldom revisit places, especially ones that exist away from usual space time"--why does it partially work there? Just revisiting itself already seems like a lot, and two day windows at a time doesn't seem like a great amount of bonding in prior visits, especially if one day is just dedicated to being examined or passing out from the fatigued life of the road.
I suppose we're suppose to engage with the idea of a sort of "distance makes the heart fonder" in that both of them are constantly thinking about the other, but the protagonist again pines about some of the wild travels he goes through nonetheless.
It felt like it was afraid to commit to the implications of the shared curse and how that would inform the ending, by discovering a new rule of the curse out of nowhere (that seemingly the mighty magician couldn't possibly fathom before in any capacity?), and I think having that shared tether would have made the fear of not seeing one another again more poignant-- "I can't stay here lest I hurt you too. Of course you wouldn't want to see me again. i stole away another place where you could rest" etc etc. The reaching for "you want me to leave because I hurt myself" doesn't quite work as a logical conclusion, for me.
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Story asides: Cursed mark? Alright naruto fan.
Gizmo feels out of place, especially in light of the more archaic tongue of the piece (the first known use seems to be in the 1940's per my googling of the etymology). I think there are other similar terms you could have used that wouldn't feel so "artificial".
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Presentation: The first bit pops off very hard in a pseudo-comic format, and then it transitions into still lovely sprite work. It's a bit curious to do that instead of like, spreading the cgs more throughout.
The custom music felt very appropriate, and I appreciated all the transitions, and the woof was cute in any form he took (cg or sprite).
I didn't quite get why he took off his coat given he was in the tower already, but it wasn't like I was upset to see his arms :p
Creativity: I feel like this felt afraid to commit to explore further, especially in having a boy fail protagonist (at least, he felt like that to me). I think maybe some explicit application of the theme might have found a way to carve out more space.
Overall thoughts: A cute story with a lot of effort put into it (i was really impressed with the cgs, transitions, cutes sprite, etc), but the narrative has both some clunky wording (for me) and focus. It didn't feel like it sufficiently resolve the tension in what I think is a matter that goes towards where the work was aiming, but delays it with a half smile and avoidance of the "promise" of suffering at the start.