This is the 360th most frequent Japanese word.
東
East.
Here, "東" defines the cardinal direction guiding the movement.
東に向かって進み続けます。
We will keep moving eastwards.
Here, "東" (east) specifies the direction of the sky that is described.
東の空が明るくなってきた。
The eastern sky has started to brighten.
In this case, "東" is used as an adjective to describe the region (eastern countries).