Spoiler warning for Land of the Lustrous
One of the central themes in Land of the Lustrous is purpose. From start to finish, all of the anime’s drama grows out of Phos’ search for some kind of purpose. That may seem like a more abstract or philosophical goal, but having a purpose is crucial for all of the gems.
Since they’re not biological creatures, the gems in Land of the Lustrous are nearly immortal. They can be completely shattered and still recover just fine as long as all the pieces are put back together. They absorb energy from sunlight, so they don’t need to eat or drink, and they don’t have any other physical needs. They also live for hundreds, if not thousands, of years, which means they have nothing but time. That may sound like a perfect existence, but it’s actually a sad one. What do you do when you live forever and don’t need anything to survive? What do you have to motivate you? Why even bother? The gems avoid this existential anxiety by each finding a purpose in their small community. Bort and many others fight off the Lunarian attacks, Rutile repairs gems who break, Jade coordinates the other gems, and everyone else has a role of their own. The only ones who don’t have this are Phos and Cinnabar. Phos is too weak to fight and can’t find anything else they care about, while Cinnabar is similarly fragile and secretes mercury that’s toxic to the other gems. For Phos and Cinnabar, finding a purpose is more than just having something to do; it’s a way to find value in themselves.
Though they may hide it, Phos’ upbeat energy and Cinnabar’s irritable attitude are both ways to hide their own sense of inadequacy. Ironically, the gems don’t seem to see any inherent value in themselves. They always need some external purpose to get any sense of self-worth. When Phos is briefly captured by Lunarians and escapes, their first reaction upon seeing Cinnabar isn’t relief at being found, it’s guilt for not finding a purpose for Cinnabar. Phos doesn’t spare a thought for themself, only for Cinnabar.
Similarly, Phos only starts to change as a person after failing to save Antarcticite. Once again, Phos is motivated more by external factors than a desire to be better for their own sake. Phos sees learning how to fight or finding some other purpose as a way to be happy with who they are. However, things don’t go the way Phos expects.
After losing Antarc and gaining gold arms, Phos becomes one of the best fighters out of all the gems. They obtain everything that they once desired, but it comes out hollow. Fighting Lunarians and being useful was always Phos’ goal, but they quickly discover that fighting doesn’t make them happy or fulfill them; it’s just work. The core issue with the way Phos and the other gems view themselves and their own value is that they always base it on something external.
Even when it’s something they enjoy doing, the gems’ primary goal is always to earn Kongo’s approval. Even though he doesn’t make them do anything and seems to care for all of them, the gems still treat Kongo as a father figure and base a lot of their self-worth on him. Antarc’s last words before being captured were asking Phos to make sure Kongo doesn’t get lonely, and even Phos plainly says that they want to fight so they can help Kongo. Their gratitude is understandable; Kongo’s the one who took them all in after they were “born” and protected them from Lunarian attacks. Even so, basing one’s entire self-worth on something like that never ends well. By the end, Phos has begun to question Kongo, but still hasn’t quite moved into valuing themself. If Phos is ever going to come into their own, they’ll have to someday find value in themself, not in an external purpose like helping Kongo or finding a job for Cinnabar. It remains to be seen if that will ever happen, but finding their own self-worth is going to be Phos’ true purpose. Even if they don’t know it, that’s where their journey is taking them.