Can’t get this platonic soulmates PHM idea out of my head.
The base idea is that you learn your soulmates native language at the same rate they do. So if you have a soulmate that speaks the same language as you, you both learn the language faster. If your soulmate speaks a different language than you, then you randomly understand a different language growing up.
This is true for humans, and this is true for Eridians, but Eridians don't know they have soulmates because (as far as I know) all Eridians speak the same language so they just think they're all very quick at learning language. That's why when Rocky is slower than everyone else, people think it's a little odd but oh well, he's just picking up on the language a little slower than everyone else no big deal.
Rocky doesn't even know he understands English. Not until he meets Ryland Grace, that is.
But what about Grace? Well, everyone on Earth assumes he doesn't have a soulmate. He doesn't learn English twice as fast, nor does any language his parents plop down in front of him make any sort of sense. They think maybe he's just older than his soulmate, that happens sometimes (and familial soulmates exist, sometimes your soulmate is your child and they are able to understand your language just as well as you do).
But Grace never settles down, never has kids (unless you count his students), and never learns any other language or pick up on slang that the younger generation is using any faster than the rest of his fellow teachers. So he probably doesn't have a soulmate, which doesn't bother him that much. No, really, he's fine with it. Besides, he is really good with music, so it feels like a fair trade-off.
Grace since the moment he was plopped in front of an instrument (a drum set most likely or a xylophone) he was able to play it expertly. He was also very insistent that all instruments were really words and he could understand what they were saying. He learned his first curse word in music class because Hot Cross Buns is very vulgar, actually.
He also cannot stand most music with lyrics, as the instrumentals and the lyrics are often contradictory and don't flow well together. He likes music without any lyrics, but absolutely loathes AI music and is always able to tell because AI music is always just a bunch of nonsensical words, whereas other music always tells some sort of story (even if it's sometimes a silly one).
But yeah, Grace doesn't have a soulmate but he has a thing where he can hear words in music and can pick up any instrument really quickly, so he feels like it's a fair trade-off in life. He was never interested in a soulmate anyway, the idea that he would love someone in that way made him uncomfortable (he knows platonic soulmates are a thing but that doesn't mean that's what he expected to get, or at least he wasn't supposed to hope for that).
So Grace lives his life, helps with the Project Hail Mary Project, goes to space, loses his memory of anything, and meets an alien who he understands immediately and who also understands him back. And Grace doesn't understand at first, gets a flashback of soulmates and that he didn't have one, but then has to explain to this alien lifeform what soulmates are when he barely understands it and...
Well, Rocky and Ryland both wish that astrophage never happened to their planets, but are also grateful for it happening so that they got to meet. And Ryland deciding to spend the rest of his life on Erid ended up not being that tough of a decision, even though he still asked to think about it.
