Later, when the Chimei general Fan Chong (樊崇) temporarily submitted to Gengshi Emperor's authority after Gengshi Emperor overthrew Wang Mang, Liu Gong accompanied Fan to the capital, Luoyang, and was created the Marquess of Shi to inherit his father's title.
The 14-year-old Penzi was greatly scared when he saw all of the generals bow down to him, and he tried to destroy the lot he drew by chewing it in his mouth, but it was in vain; he was selected.
Even after his selection, however, he had no power and remained a cattleman until the Chimei forces defeated Gengshi Emperor and entered the capital Chang'an later that year.
Initially, the people of the Guanzhong (關中, modern central Shaanxi) region submitted and offered tributes, but were surprised when the Chimei soldiers continuously robbed them on the way to Chang'an.
Soon, the food supplies were completely depleted, and the Chimei forces burned many Chang'an palaces and other buildings and pillaged the city, then marched west into the modern eastern Gansu region.
After battles of attrition against Liu Xiu (Emperor Guangwu)'s forces, they were completely drained, and they surrendered to him in spring 27.
Emperor Guangwu made Penzi an assistant to his uncle Liu Liang (劉良), the Prince of Zhao.