東国 Azuma.【追儺 Tsuina Ceremony 】14

Higashikuni refers to the eastern provinces as seen from the capital.
In this period, the capital was Kyoto in today's Kansai region, so
the zone that went east from Kyoto.
Kanto, near Tokyo.

The range seems to change with the times. In the Jomon period
It refers to the area east of Echigo, Shinano, and Mikawa provinces.

From the Asuka period onward, from the eastern side of Mino, Shinano,
and Toe provinces to the border with the Emishi world.

From the time of Emperor Temmu (Asuka Period),
the Tokaido countries began to be called “Azuma” or “Azuma-no-kuni (Eastern Province)”.