I know, huge surprise right. 

I couldn't believe it too when I first heard about this. I thought Kimura would flunk badly cuz, how many people out there can act convincingly as a Prime Minister?!

But let's not jump the gun. 

To keep the long story short:

Keita (Kimura) was an elementary school teacher in Nagano and his hobby was star gazing. His father and elder brother were politicians, but they passed away in a tragic plane crash. Keita was roped in to run for elections, which he did but his original intention wasn't to win. 

But he did. 

Thereafter there are plenty of unseen political powers at work to make Keita the Prime Minister instead.  Primarily, the mastermind of all these is Kanbayashi - the House secretary of the ruling party. Keita was to become the puppet of the more experienced politicians, specifically Kanyabashi. 

However, the sincerity and hard work of Keita soon won over every sceptic and as Kanbayashi found out, he was not a puppet on his strings. Kanbayashi had to come up with another scheme to destroy Keita. How far would he go to realize his ambition? Could he succeed?