I'll start with the obvious. The presentation of this is gorgeous. Custom gui, music, cgs all built to the tone of the piece. The hard work was obvious and shows. The chase scene? Fantastic. Felt like something you could see in a museum.
The piece brings to mind an essay had I had to read in college-- some sort of excerpt from a work that trying to find on the internet without any of the additional context makes nearly impossible-- titled Sentiment Always, Sentimentality Never.
The short of it is the sentimentality felt unearned, but let me circle back to that. Let me take the long way around, not unlike the story in itself :p
There was some characterization issues to me. Or rather, Mori's beginning felt detached with the rest of Mori. We start off with Mori detached, seemingly having already mourned his death, expecting to have passed in one year but malingered for four. He has a sort of clinical detachment from his body, ready to watch his body get burnt to a crisp, and yet with the prospect of going into a place of paradise, he agrees to Memento's ask to linger and go through his history. It feels like a choice born of progressing the plot in contrast to the opening scene.
We do however, move to a more consistent viewpoint of Mori from there-- one that didn't do the mourning his detachment implied-- it's more of an artifact of the opening feeling separate from the the rest of the characterization.
Similarly, you set this piece in conversation to the Death of Discworld and the Death of Nail Gaiman's works (especially with what feels like the nod to Stardust by Neil Gaiman in the "play within the play which frames with a similar structure against the greater plot narrative). Discworld's death is kind of the detached end of the spectrum. He tries to learn via adopting a child and then eventually raising his grandchild (after his child passes on). Death isn't quite robotic in Discworld as the auditors but he's more of structure of a natural force. I'm not as well versed in Neil Gaiman's death, but I believe his endless are more "human", having more earthly attachments and emotionality.
Memento sits somewhere in the middle, but he simultaneously flickers between both ends of the scale. He questions Mori "what is joy, what is grief", etc etc, while also pointing to elements that he believes causes them (belly rubs, a flower, a sunset). His understanding and his uncertainty (of needing to define his own existential dread) feels sorta inconsistent. Some of his wording felt robotic, but then the expressions were too vivid. Discworld's death would have the flat skull affect, but Memento here is living it up, showing the depths of expression (which are lovely, mind you, but feeling incongruent to his lines).
In that same vein, it feels sorta unearned that Memento fawns over Mori. He's indicated he's spent like lifetimes observing deaths and talking for various periods-- we spent just as briefly a window with Mori and we saw a play in which his own focus was narrowed on the Memento's foil (which would resonate more if we could have Memento identifying with that same sort of Stardust vibes) but we get the simultaneously wizened, detached Memento (which ALSO sort of echoes to like Phos as we approach the end of Houseki no Kuni (spoilers~)-- someone that has overcome worldly desires). His fawning is where we start to feel that sentimentality (or I do). An informed reason for obsessing over Mori. The forced crying (and some of those caps locks moments felt unearned).
I think we could have buffered this out if we had less of the play and the more of the running sequence. The foil narrative where we lingered with Stella for so long (her name the path of least resistance for Star -> Stella) has the payoff of Mori lashing out at her when she briefly revisited, if anything portraying her as sorta callous and dismissive (of which as a character we're trying to have her foil against for Memento isn't quite the best payoff?). She's perhaps being given an excessive response but the burden of caring is sorta with the living, not the deceased (like a funeral). He's all but dead but in execution. She's not properly understanding him and not is leading her interaction by trying to connect via the offering of herself, as opposed to letting him lead (paralleling to how he has to be the one comforting her backstage-- even her offered assistance starts with pulling back to herself).
The running sequence-- the inevitability of Memento's approach? Gorgeous. I think if we had MORE of that (sorry, more hard work for Arcadia) it would help draw in the inevitability. A place to buffer the conversation with each stop as Memento catches up. It's the proper lead up to the nothingness, but we don't get enough time for it to sink it. It's kind of a snapshot that Memento was lying. The more time we run, the more time we have to be running from the horror, for it to build up at the back of our minds-- what must be avoided looms in its absence, a sort of negative space. This was already perhaps the strongest part of the piece, especially in its presentation, but I think that makes it hurt for how brief it was. I kinda wanted like the rule of threes: three distinct places to see the inevitability of Memento as opposed to what felt like the one sequence.
Back to sentimentality-- the dog Mori always wanted (with that obvious presence as Memento) was yet another moment. We revisited his waking life, but we don't get it until the end of the flashback sequences? We couldn't have a hint of it earlier? It feels like a justification for the romance with Memento-- even his picking of Mori feels like "My wolf by default. I chose you as my sample person for my existential dread because?" He's seen endless people and this one experience is the one that draws him in? The memory viewing of the play helped him subtly notice himself via the similar being of the star? It doesn't feel convincing to me that Mori is the one that broke the damn on Memento's feelings.
However, I did love how the waltz worked as a medium for Mori to have his performance (calling out the stars as the audience-- what greater stage is there than the universe itself).
Ugh, I've already said a lot, so if you have further asks like... let me know, but I don't want to say that this still isn't an excellent experience. The music is a lovely counterpart to the ethereal scenes, punctuated with fluid transitions between them all. It really does show the strengths of all of the team that contributed to the project, and is a fantastic contribution to the May Wolf experience. It's not surprising why it got the feedback its received. It's merited, even if I can't help but pick at the tangled skeins. Time for me to depart this comment~