You Do Need power plug adapter while traveling from Nigeria to Kiribati.

Here is Why You Need An Adapter

The outlet and plug type used in Kiribati is I and in Nigeria are D and G. This is how they look like.

Nigeria

In Nigeria, outlets of type D and G are in use.

Type D

Type G

Kiribati

In Kiribati, outlets of type I are in use.

Type I