I can’t tell, is that really an anti-human sentiment that we ended on? There’s definitely a bit of self-sacrifice on the part of phos, which is fine, but machine brother carrying them to the end feels wrong.
Kinda, yeah, but it's sort of been there from the beginning. The Pure Land Buddhism that inspired this story usually views our current era as being spiritually corrupt or degenerate, and is aiming for a sort of Return to
Monke Buddha in the Pure Land.
So in very broad strokes the plot of Land of the Lustrous in chronological order seems to be something like this:
1. Ayumu invents Adamant's older brother (who I'm just gonna call Aniki from here on out for brevity's sake), who is an AI that just really wants to make his mom happy. This is bad because his mom is Ayumu, and Ayumu is a nihilistic psychopath.
2. Aniki smashes a meteor into Earth because he wants to impress mommy dearest, and mommy hates her boss who takes credit for her work and looks at internet porn, so Aniki decides to kill him in a flashy way. This leads to a cascade effect that brings about the end of humanity.
3. Aniki gets dismantled, but Ayumu seals up his hardware and sets it afloat in the ocean rather than let him die. Apparently his little omnicidal stunt actually did impress her.
4. Humanity realizes they're fucked and invents Adamant, who is a prayerbot who will guarantee that they get to move on to Buddhist heaven even after there aren't any people left to pray for the dead. This completely misses the point of enlightenment, but refer back to the opening paragraph about modern humans being a bunch of spiritual degenerates.
5. Humanity dies out, Adamant prays them away until he breaks and can't pray anymore. The remaining humans become the Lunarians, who are basically just the worst of the worst humanity had to offer, since they were having Adamant pray them away in the order of most to least virtuous and when he broke only the absolute dregs were still left.
6. Gems and Admirabilis show up, becoming the new sapient life forms on Earth. This
should be the start of a new, better spiritual age, except the remnants of the old, shitty era of humanity (Adamant, the Lunarians, the ice floes) completely fuck up their development. The gems end up looking human by patterning themselves on Adamant, the Lunarians make them become a militaristic society by attacking them, and the non-militaristic Admirabilis end up enslaved by them. Basically the new era ends up looking a lot like the old, degenerate era, but with a lot more androgynous gems.
7. The, uh... plot happens. I'm not gonna summarize all this, you just read it. Let's fast-forward to the last few chapters, after Phos turns into an amorphous white blob.
8. A new sapient rock species shows up. Buddha-Phos offers to make it more human-like by making it ambulatory and giving it vision, but the new rock is all like "Nah buddy, I'm good. Thanks for the offer, though." Phos doesn't insist, and just chills with the new rock for millions of years. In doing this, Phos is deviating from Adamant's approach of becoming the spiritual leader of the new era, and there aren't any Lunarians to fuck everything up this time.
9. More new rocks show up, and now we've got a society going again. Phos stays hands-off for the most part. The rocks think Phos is cool, but they don't have some sort of borderline-deification of him going on like the gems had with Adamant. New rocks stay ambitionless and spiritually pure.
10. Oh shit, Aniki's back! Except he's a lot more chill than he used to be, gives us the backstory, and agrees with Phos that humanity sucked and shouldn't be allowed to get their degenerate ideas into the heads(?) of the new rocks. He tells the rocks the story of humanity and the rocks are all like "Cool story, Aniki" and keep doing their rock thing. Aniki turns out to be pretty sympathetic and actually a pretty nice guy when he's not trying to get his shithead mom to love him. Just don't ask him his opinion on internet porn.
11. Sun go boom, Aniki loads the new rocks into the spaceship, takes the last remaining part of the original rock Phos with them, while Earth and the remaining human-ish part of Phos gets obliterated in cleansing nuclear fire. This mostly wipes out the last vestiges of humanity.
12. Whoops! Aniki overshot the planet the Lunarians wanted them to land on! Looks like they're not doing what the Lunarians
wanted them to do, and are instead landing on a completely uncharted,
pure planet! It's a whole new
land for them to live on unknown to humanity!
13. Fast forward to the final chapter: Aniki's dying, Phos is still a tiny rock, all the other rocks are still doing their rock things on geologic time scales. With Aniki's death the last vestige of the former degenerate spiritual era is gone; the rocks are starting fresh with the slate wiped clean. The real Land of the Lustrous was all of the friends we made out of rocks along the way of suffering for billions of years before finally being cleansed of our sins by the death of the sun.
tl;dr
Aniki did nothing wrong; Ayumu and the Lunarians ruined everything by not knowing when to just let the fuck go and allow a new spiritual era to start. Aniki's basically just an innocent trying to please someone he doesn't realize is a bit of a monster, which is why he's cool to jump-start a new spiritual era once he's free of human influence.
Yeah, I wrote all that shit to defend the honor of a genocidal robot eyeball because I thought he was funny. Fight me.
