The characters of the man and his wife in this Japanese folk tale are clearly two dimensional and flat characters rather than fully developed round characters. This is perhaps their only similarity, as after this the characters diverge sharply in terms of their characteristics and qualities. It is quite common for characters in folk tales to be flat and undeveloped, as often they can function allegorically, representing wider concerns or qualities.
This is certainly the case with this folk tale, as the old man clearly represents good and his wife the dangers of greed and jealousy. Notice how these key qualities and the differences between the man and wife are identified in the very first paragraph of the story:
A long long time ago, an old couple dwelt in the very heart of a high mountain. They lived together in peace and harmony, although they were very different in character, the man being good-natured and honest, and the wife being greedy and quarrelsome when anyone came her way that she could possibly quarrel with.
This quote clearly indicates the key differences between the man and his wife, whilst at the same time also signalling the similarities. With such an introduction, it is clear that this will be some sort of tale that shows the benefits of being good and the dangers of being evil.