What technological cultural or military advancements have reached the uncivilised japanese through korea?
A lot of cultural aspects filtered through Korea to Japan from China. Examples of this include Buddhism, Confucianism etc. although that is debatable as it is questionable how much direct access Japan had to China. The best example I can think of is mounted warfare, Japan attempted to invade Korea sometime in the first millenium and got beaten by Korean horsemen, this then led the Japanese to create mounted archers as shock troops who later became the samurai. What I understand mainly is that Korea acted as the medium between China and Japan, so all the technological improvements from China, for example wet field rice agriculture etc. was most likely transferred through the Korea.
