what if the reason nobody can tell fred and george apart is because they really are interchangeable
not in a ~it doesn’t matter~ way but like. molly and arthur used to worry that fred and george might turn out to be squibs because they weren’t doing any accidental magic as children, but they were, THEY TOTALLY WERE, it just wasn’t anything flashy, instead they were just like idly switching bodies all the time
and like sometimes it doesn’t make much of a difference, whatever, wake up in the opposite bed you went to sleep in, but it gets like dangerous and weird if you’re on a broom or in the pond or letting your mum teach you to cook or trying to be mad stealth, so for a long long time everybody presumes they’re clumsy maybe-squibs and that they’re doing their twin lying thing when they try to explain what’s going on, so they learn to handle the issue their ownselves
they just. don’t go anywhere without the other. they start each day deciding which body is going to be which (because at this point they really don’t know which body is technically fred and which is technically george), and they learn to reorient FAST when they switch, and what things set them off, and eventually they learn how to act like nothing’s up even when one of them’s in the air and one’s on the ground or whatever, and then they burn past that til they can finish each other’s sentences — til they can switch midsentence — til they can play beater together — til they can switch in a split second in the middle of a game — til there’s room for other kinds of accidental magic to start showing up
at hogwarts they keep each other awake in history of magic by switching back and forth. in potions they take turns brewing and keeping lookout for the slytherins. in transfiguration and charms they keep their grades up because one of them will always get a spell right on the first try so they switch and make it look like both of them do and then they practice on their own later in private. it keeps the mystery alive.
at first they thought lee was just a lucky guesser but no, lee can always tell one twin from another twin — it’s not exactly telling fred from george, because while they are definitely two distinct personalities neither one of them feels like fred all the time or george all the time — but lee knows who he argued with yesterday or who he lent his notes to or who’s best to ask for help in astronomy and who’s best at runes.
the weasleys are pretty bad at it for the longest time, but then bill comes home from his first year cursebreaking and he can tell, and over a holiday he teaches his trick to charlie so charlie can tell. alicia and katie and angelina can tell. the twins honestly don’t know if oliver can tell or not; so long as they’re doing what they’re supposed to on the quidditch pitch he doesn’t really care about much else. harry can tell. luna can tell. tonks can tell.
the problem is there’s no way for this to end happily
YES THERE IS
THERE IS INDEED A WAY FOR THIS TO END HAPPILY LISTEN UP
so after fred dies, george hates being trapped in one body, feels claustrophobic, misses fred so much he thinks it might drive him insane
but then one day
george blinks and he’s somewhere he wasn’t a second ago, he’s in a place full of white light and he can’t orient himself, can’t ground himself, feels dizzy and sick and overwhelmed but it only lasts for about thirty seconds.
then he’s back in his own body.
and he looks down at his chest, his legs, his arms, there’s an ear missing so it’s definitely still his living body, but there’s something written on his arm, scrawled in messy quill ink.
"i love you. i miss you."
george flips out, washes off the ink and immediately writes a message in reply— “how’s death going?”
he walks around with that message written on his arm for weeks, always keeping a quill pen somewhere nearby, waiting, waiting, before it finally happens again. the switch. george is alive, so he can’t handle being in the afterlife, he feels dizzy and sick and it’s the worst feeling in the world, but it doesn’t last long, and when he gets back to his living body, there’s a long message from fred waiting on his right thigh, the ink still drying.
this goes on for years, never as often as either twin would like, but it’s enough. fred helps george figure out how to propose to angelina, fred helps plan the wedding. sometimes it’s fred in george’s body when angelina kisses her husband. sometimes she suspects, but she doesn’t mind in the slightest.
it gets easier as george gets older. the times when he switches into fred’s afterlife don’t hurt as much. he almost feels comfortable there, almost feels oriented. he knows he’s getting closer to dying.
then when george is past ninety, lying on his deathbed, he writes a careful message on his palm. “i’m coming soon. where are you?”
they switch, it lasts for almost five minutes this time, and when george gets back into his own body, he sees the instructions fred wrote over his heart.
"you’ll wake up in king’s cross station. take the second train and get off at the third stop. i’ll be waiting."