Peach Boy Riverside manga volume 9 features story by Coolkyousinnjya with art by Johanne.

Long, long ago, there lived an old man and an old woman. The old man used to go and cut grass for the farmers around, and the old woman, his wife, went to the river to do laundry...but this isn't Mikoto's past. This is a journey down memory lane to learn how Kibitsuhiko-no-Mikoto, also known as "Momotaro," met Mikoto and how they parted. What will be revealed in this flashback about the relationship between the two Mikotos?