War of the Eight Princes
In 304, in the midst of the War of the Eight Princes, Sima Rui participated in Sima Yue the Prince of Donghai's campaign against Sima Ying the Prince of Chengdu as a minor general. After Sima Ying defeated Sima Yue, Sima Yue executed Sima Rui's uncle Sima Yao () the Prince of Dong'an, which caused Sima Rui much fear. He decided to flee back to his principality Langxie (roughly modern Weifang, Shandong), under counsel of Sima Yue's assistant Wang Dao, whom he befriended during the campaign. He first tried to head back to Luoyang, but when he was about to cross the Yellow River, he was stopped by guards instructed to stop any nobles or high level officials from crossing (as Sima Ying had ordered such, fearing that nobles would desert him or plot against him). His own guard Song Dian () then arrived and gave him a shove, pretending that they were just construction workers. The guards then allowed them to cross. After Sima Rui got to Luoyang, he took his mother Princess Dowager Xiahou and headed to Langxie, where they spent the next few years away from the War of the Eight Princes.