Rather than wait until the year after the preceding Emperor died to change the name of the era which was the custom, the new Emperor changed the era name into Dodai and tightened the budget that had loosened while Kanmu had conducted frequent military activity against the Siberian invasion and moved the capital, and actively worked on organizing redundant court positions, placing of a Kansatsushi, where Daijokan directly watches over regional government and abolishing Sangi, but he was sickly from a young age and abdicated the throne to the Crown Prince Kamino (Emperor Saga) in 809.
新天皇が先帝死去の翌年になるのを待って改元する先例に反して即位後ただちに大同(日本)と改元し、桓武がさかんに行った蝦夷侵略の軍事行動や遷都にともなう土木工事のために弛緩した財政の引き締め、機能していない官司の整理、参議を廃止して太政官が地方政治を直接監督する観察使を置くなど積極的に政治改革に取り組んだが、若いころから病身だった彼はやがて体調を崩し、早くも大同4年（809年）には皇太子神野（嵯峨天皇）に譲位することになった。