Natsume helped a spirit Tsukihigui. Tsukihigui makes him younger in return fo...
Natsume's Book of Friends
Season 6 Episode 7: Gomochi's Benefactor
Natsume is surprised when a youkai comes to seek Reiko in gratitude. Years ago, the youkai's to-be-bride received freedom from her help, and now is about to be wed. They invite Natsume to the wedding.