Question: What were the consequences for Japan of the failure of the Mongol conquest ? 

My first reaction is that it was not important — it failed; first in 1274, and again in 1281. The Mongol invasions do not play a similar role in Japanese History as in the parts of Asia where the Mongols succeeded. However, on the flip side, the defeat of the Mongols affected Japanese society at the time in significant ways. The Kamakura Bafuku expended considerable resources in developing defenses. Alliances were forged and power redistributed. Bakufu leaders expended a lot of energy in the defense of Japan against the superior Mongol force. Ultimately, such efforts weakened the Kamakura.

When I say the Mongol defeat was unimportant, I must qualify that it became important well after the fact. The ways historical information have been used during the twentieth century provides an additional dimension. The defense has been cited as an early incident of Japan as a unified place, where regional lords combined resources to defend Japan as a unit. It becomes a powerful historical moment "proving" the presence of Japan as a unified single place. The defeat of the Mongols has become part of the national memory, used to depict a unified and always existing Japan, from Jimmu (first mythical emperor and founder of the imperial line), to amalgamation of clans under the hegemony of the Yamato during the seventh century, followed by the thirteenth century repulsion of the Mongol "hordes."

The Mongol invasions also provide a wonderful story about the kamikaze-the divine wind that magically appears and destroys the Mongol fleet. The winds (most likely a typhoon) probably came and did just that, and they were divine because they saved the samurai. The story lends support to the belief in the spirituality of Japan (and State Shinto), especially when contrasted with the rational and mechanical West. Then, the other way kamikaze becomes used is through all the suicide planes sent to destroy American ships. The Japanese used the word for the special attack corps, a suicide attack force. The name suggests that these young men represented Japan's divine spirit; they were the divine wind that would save Japan.