Ironically from what I hear the Hidan and Kakazu arc was actually rushed by suggestion of the editors. It seems Kishi actually wanted to given the Immortal duo a backstory each. I have the feeling it was probably so that we could sympathize with them.
Can you imagine feeling sorry for freaking Hidan?

The reason I liked the Immortal Arc was because the author didn't give the duo (or at least Hidan) some sappy backstory to make them more sympathetic. Kishi has a tendency to justify/redeem majority of the villains that he introduces:
1) Zabuza- behind his walls, he actually loves and cares for Haku deeply
2) Orochimaru- lost his parents at a young age, and witnessed so much death occuring around him that he became driven to seek immortality
3) Sasori- also lost his parents at a young age and became obsessed with immortality
4) Itachi- turns out he massacred his clan, purposely tortured Kakashi, and drove his brother to the brink of insanity and caused his obsession with revenge, all because he was a true hero
5) Pain- lost his parents at a young age, and witnessed so much death occuring around him that he became driven to seek world peace
6) Obito- got friendzoned
7) Madara- mistreated by Tobirama, duped out of the Hokage seat, lost the trust of his own clan, and Uchiha genetics
The fact that we finally got true villains who were complete pricks and acted without any sort of justification made the Immortal Arc that much more unique and enjoyable.
Edited by Baguette, 07 April 2013 - 05:02 PM.