You Do Need power plug adapter while traveling from Western Sahara to Japan.

Here is Why You Need An Adapter

The outlet and plug type used in Japan are A and B and in Western Sahara are C and E. This is how they look like.

Western Sahara

In Western Sahara, outlets of type C and E are in use.

Type C

Type E

Japan

In Japan, outlets of type A and B are in use.

Type A

Type B