It gets you with the frame, not the fantasy. Marielle is parked in a house high in the mountains between Switzerland and France because her body needs the clean air, and the whole thing arrives as recollection, which means every scene comes pre-tinted with the knowledge that it already ended. Memoru and her people are the least threatening aliens ever put to cel, gnome-sized crash survivors who never got the ship working again and quietly built a life on the island instead. That's the real pairing: two kids stranded, one by a broken spacecraft, one by her own lungs, keeping each other company in the meantime. One episode, 1985, and it treats that as sufficient, because it is. Anyone who sat through the TV run knows what a jewel box is actually for. You open it, and the small bright things are still in there.
Marielle is a young girl sent to a remote house deep in the mountains between Switzerland and France so she can regain her health. The tale is framed as her recollections of adventures shared with Memoru, a tiny alien girl from a nearby island whose gnome-like people were left stranded on Earth when their spaceship crashed. Released after the television series, this roughly 15-minute OVA pieces together footage from episodes 1, 2, 7, 24 and 25 into a short fantasy compilation.