I have a question though: does it have to be just The One Wish or can there be layers? For instance, in Sasha's case, while her greatest wish is to be with Alone and Tenma again, she has one as Athena and that is to end the war she left behind. The two are closely tied together so it would be hard to split the two :x
/having so much fun thinking of how to portray the wishes eeeee~