Tokyo Koutei ☆ Houjou Renka
Renka Houjou is the empress of Tokyo, which is a independent empire.
Renka Houjou is an empress that heads the empire that spreads from Okutama to the northwest, Edogawa Ward to the east, Izu•Ogasawara Islands to the south, with a land area of 2187.58 square kilometers, population 13 million.
This is the story of a regular boy Kazuto Seionji succeeding the throne of the Empire of Tokyo.
(roughly translated from the official website)
10 volumes so far as of June 23, 2013