Japanese Task Force

The Japanese Task Force, (commonly reffered to as the Task Force, or Kira Investigation Team) is the primary organization searching for Kira.

Overview
The Task Force was created by L after he deduces that Kira is in Japan, and is the only organization within the country that is searching for Kira. The existence of the organization is not made public, and the names and personal information of all of the members' is kept secret. After L's death Light Yagami heads the organization, and begins operating as 'L'.

L
L is the creator and leader of the Task Force. He is considered in-universe to be the world's greatest detective. His primary objective is to bring Kira to justice at any cost.

Light Yagami
Light Yagami is Kira, and he joins the Task Force in order to get close to L and discover his real name. His inteligence is on par with L's.