It's a reincarnation fic wherein Arthur and Percival are a couple, and Arthur "recognizes" Merlin at the school fair of their (Percival and Arthur's) daughter. It's both fluffy (the Arthur/Percival kind of thing) and painful because the situation between Merlin and Arthur is awkward, and full of memories that don't really belong to them. This is a very beautiful fic, and Percival is wonderful in his love and his trust of Arthur, no matter what.