There is a place known as "Kannagi-san" (or Kannagi Mountain), which connects the world of the living with the world of the dead. Here, beings called the "Kannagi no Tori" (or Birds of Kannagi) live, and it is their job to take the souls of the people who die to Kannagi-san, where they can then pass on to the world of the dead. The "Kannagi no Tori" get sent out just before someone dies to retrieve their soul and bring it back.
However, one "Kannagi no Tori," Ikaru, is different. He feels wrong about death, and typically when he is sent out instead of letting the death take place and retrieving the soul, he usually interferes with fate by preventing an accident, convincing someone not to commit suicide, or rescuing the person in danger to save their life. He still has not retrieved a single soul. He is given a "final mission" to prove himself as a "Kannagi no Tori," and if he fails, he will cease to exist.
His mission is to retrieve the soul of a young boy, Watanaki Ruu, who is to die in a car accident on the first of June, in about one month. Over this month Ikaru has several interactions with Ruu and his family, and feels an usual tie to Ruu, and doesn't want to take his soul... but his fellow "Kannagi no Tori" friends are trying to make sure he gets his mission done because they don't want to see their friend cease to exist, and at the same time, they have missions of their own involving people around Ruu as well.
Will Ikaru be able to finish his mission, or will he be unable to claim this soul as well...?