TASK DEFINITION: In this task, we ask you to rewrite a sentence in simple English without changing its general meaning. Essentially, you want to make the sentence easier to read by using simpler words, utilizing more straightforward sentence structures, and omitting non-essential information etc.
PROBLEM: Katerini ( , " Kateri ́ ni " , -RSB- ) is a city and municipality in northern Greece , the capital city of province of Pieria ( regional unit ) in Central Macedonia , Greece .

SOLUTION: Katerini is a Greek city which is the capital of Pieria prefecture in the region of Macedonia .

PROBLEM: He acceded to the Chrysanthemum Throne upon the abdication of his father , the now-Emperor Emeritus Akihito on 1 May 2019 at 00:00 local time ( 15:00 UTC ) .

SOLUTION: He has been on the Chrysanthemum Throne since his father Akihito abdicated in 2019 .

PROBLEM: Popular sovereignty is the principle that the authority of a state and its government are created and sustained by the consent of its people , through their elected representatives ( Rule by the People ) , who are the source of all political power .

SOLUTION:
They give their permission through their elected representatives ( Rule by the People ) , who is the source of all political power .