This long journey of more than a thousand years focuses on our main protagonist Kurou. It can be somewhat confusing at the beginning, but once you understand the plot this story can be quite entertaining.
The main thrust of the story goes like this: Kurou meets a beautiful woman by the name of Kuromitsu, and begins a relationship which transcends life and memory. Kurozuka tells the tale of a journey undertaken by immortals, and those who chase after immortality.
The majority of this story takes place many centuries in the future, after Kurou has been separated from Kuromitsu. Having lost almost all of his memories, Kurou seeks to understand why he cannot die, to rediscover his identity, and to find the woman that haunts his dreams.
One day, while he was self pondering about his life while ruining a date on a whim, he is suddenly kissed by an elementary school girl go goes by the name "Ageha", stating that she will use him to "wipe out every ghost in the world". While the sex appeal of an elementary school kid kiss was not enough to turn Genji to her side, the fact that she "bought him" by paying a huge debt that he had adcquired seems to work quite efficiently.