Later, by which time Tang had fallen and Yang Xingmi's domain, which was ruled successively by his sons
Yang Wo and
Yang Longyan, became known as Hongnong, and then
Wu. However, the power soon fell effectively into the hands of the regent
Xu Wen, as he and another general,
Zhang Hao, had assassinated Yang Wo, and he then killed Zhang and supported Yang Longyan as Yang Wo's successor. As Li, as the prefect of Run, had a habit of visiting the area outside the city at night, Xu came to suspect him of plotting against Xu's governance, and therefore moved him to Jiang Prefecture (江州, in modern
Jiujiang,
Jiangxi). Realizing that Xu suspected him, Li sent his fourth son
Li Jianxun to pay homage to Xu. Xu was impressed by Li Jianxun's studiousness and believed that this showed Li Decheng was not intending rebellion. He further gave a daughter to Li Jianxun in marriage. Li Decheng was later made the military governor of Weiwu Circuit (威武, somewhat of an honorary title, as Weiwu was traditionally headquartered in modern
Fuzhou,
Fujian, then under the control of Wu's southeastern neighbor
Min) and put in charge of Fu Prefecture (撫州, in modern
Fuzhou,
Jiangxi — not the same Fuzhou as Weiwu's traditional headquarter site). While he was at Fu, there was an occasion when the arrogant junior regent
Xu Zhixun (Xu Wen's oldest biological son), hearing that Li had many singing girls in his household, demanded that Li give some to him. When Li responded that these singing girls were too old for Xu and that he would try to find younger and more beautiful ones for Xu, Xu responded to Li's messenger, "One day I will kill Li Decheng and take even his wife!" (However, this threat was never carried out, as Xu Zhixun himself was thereafter assassinated by the general
Zhu Jin and replaced by his far more civil adoptive brother
Xu Zhigao.) Song also apparently wrote a letter to Li, trying to stop him. However, Xu soon accepted the throne, ending Wu and starting
Southern Tang. == During Southern Tang ==