Emperor Seimu

was the 13th emperor of Japan, according to the traditional order of succession. Historians consider Emperor Seimu to be a legendary person, and the name Seimu"-tennō" was created for him posthumously by later generations.
No certain dates can be assigned to this emperor's life or reign. The conventionally accepted names and sequence of the early emperors were not to be confirmed as "traditional" until the reign of Emperor Kammu, who was the 50th monarch of the Yamato dynasty. 
Traditional history.
Seimu is almost certainly a legend; but the "Kojiki" and "Nihonshoki" record his name.
Events of Seimu's life.
The limited information about Seimu does not imply that no such person ever existed. Very little information is available for study prior to the reign of the 29th monarch, Emperor Kimmei. 
After his death.
This emperor's official name after his death (his posthumous name) was regularized many centuries after the lifetime which was ascribed to Seimu.
The actual site of his grave is not known. According to the Imperial Household Agency, this emperor is venerated at a memorial Shinto shrine ("misasagi") at Nara.