Theory:

Once there lived a good old couple in Japan during the nineteenth century. They were childless and had a pet dog named Muko. Since Muko was their beloved pet, they treated it like a kid and showed more love and care. One day, while accompanying the good old man, Muko spotted a place and compelled its master to dig there. When the good old man started digging in the location specified by Muko, he was surprised to find a pile of gold coins buried underneath the ground. Thus, the good old couple become rich overnight and the kind-hearted couple distributed a large portion of their riches to their poor neighbours.

However, there lived a bad old couple in the same village who were known for their wickedness and greediness. When the wicked couple came to know about the good old couple's fortune, they forced Muko to find a treasure for themselves as well. Muko was scared of the evil couple and showed a place under a pine tree with a dead kitten buried inside it. This enraged the wicked pair, who killed Muko as a result.

When the good old couple came to know about their pet dog's death, they went to its grave and mourned for its loss. On that night, Muko's spirit appeared in the good old man's dream and asked him to create a mortar and mill out of the pine tree from his grave. The good old couple designed a mortar and mill out of the pine tree as instructed by Muko and used it to prepare rice pastry and bean sauce during the new year. Magic happened as the dough mass inside the mortar was transformed into a heap of gold coins, and each drop of bean sauce from mill was changed into gold bits. The bad old couple secretly noticed the magic from the window and borrowed the magical mortar and mill the next day. Unexpectedly, the magical mortar and mill gave out a foul mass of worms for the bad old couple. This arose their anger, and so they destroyed and burnt the mill.
 
Muko's spirit once again appeared in the good old man's dream. It explained the incident and asked him to collect the ashes of the magical mill burnt by the evil couple. Also, it asked him to throw the ashes on the withered cherry tree, assuring that it would bloom. The kind old man trusted his dream for the second time and performed the tasks as instructed by the dog's spirit. Magic happened again. The withered tree bloomed with the ashes sprayed.

The good old man came to know about his lord daimio's arrival and wanted to greet him. Despite the officer's instruction to kneel down before the procession, the good old man positioned himself on a cherry tree and threw ashes on it, which started to bloom while the daimio neared the tree. He was pleased to see the old man's magic and rewarded him with many gifts.

On having learned about the incident mentioned above, the wicked old man went near the procession to perform the same magic with the remaining ashes he had collected. Unfortunately, the ashes did not do any magic and, he was beaten up to death as he spoiled the procession with ash particles. The wicked man died. The good old couple happily lived long with the wealth gained.