He Traveled Through Time and Became the Shogun, but He Wanted to Save the Southern Song Dynasty

During the Southern Song Dynasty, Japan's Kamakura shogunate Minamoto no Tomo admired the Song Dynasty. In 1217, he hoped to sail west to the Southern Song Dynasty to become a commoner. However, the boat ran aground and the trip failed. In 1219, Minamoto no Tomo was assassinated. What would have happened in history if that ship had not run aground? Traveling back to the Minamoto Dynasty in 1217, how to return to the Southern Song Dynasty, and how to survive in the face of death. After losing his teacher, brother, and lover one after another, how could he cheer up and support his monarch, bravely fight against the powerful ministers, and save the Southern Song Dynasty, and even establish an East Asian anti-Mongolian front? Can he succeed, and can he return to modern times?