Guy becomes immortal after kissing a girl I am looking for the name of a certain anime I saw when I was younger. It was about a guy who was fleeing into the mountains for some reason. In these mountains he found a woman. After kissing her he found out that he became immortal and lived for thousands of years. I also remember that the moment they kissed he would feel inhuman pain for 3 consecutive days.

Edit: 
I can't properly remember the art style or the music used. I am sure it was a series around 12 episodes. I watched it subbed and don't believe there was any dubbed version (I don't really watch those so didn't pay attention to that). I believe it was a Madhouse production but I can't tell that for sure. The moment I started watching it had just about ended and I believe the end was a bit of a vampire-like story or at least hinted at a vampire-like plot.

I remembered a bit more about the plot: it was set in medieval times between 1200 and 1400, I think. But halfway through the plot, he loses consciousness and stays so for 1000 years and ends up in a post-apocalyptic Japan where he starts to search for his beloved (the one who kissed and made him immortal). Also it was not 2007 when I watched it but the end of 2008. I read the manga in 2007.
This sounds somewhat similar to Kurozuka.


  The series begins in 12th century Japan and centers on Kuro, a character based loosely on the legendary Japanese swordsman Minamoto no Yoshitsune. Kuro and his servant, Benkei, meet a beautiful and mysterious woman named Kuromitsu while on the run from Kuro's elder brother, who seeks his life. Kuromitsu and Kuro fall in love, but he soon discovers that she harbors a terrible secret: she is a vampiric immortal. Following an attack by his pursuers, Kuro is badly injured and must imbibe Kuromitsu's blood to save his own life. Kuro is then betrayed and attacked by Benkei, who has been subverted by a shadowy organization called the Red Army, and Kuro's head is severed, which interferes with his transformation into a fully immortal being. 
  Kuro loses consciousness and wakes up centuries later in a post-apocalyptic, dystopian Japan. The surviving citizens have fallen under constant oppression by the Red Army, and Kuro is quickly found and recruited by an underground revolutionary movement called Haniwa. The remaining episodes follow Kuro's fight with the Red Army and its host of elite warriors, who have been enhanced by samples of Kuromitsu's blood, and his quest to find his inexplicably lost love.


The anime is also by Madhouse from 2008.