Although the show itself has not lived to the initial hype and has a bit of a flop in the middle, the end represents an ultimate mindfuck. Just one of the best there is! I think the last episode is well worth the time spent for the series. I've really enjoyed it. Pure tainted love. So wicked it is just scary. I've still got chills down my spine when i remember these words by Kuromitsu("don't be afraid"). Women can be terrifying, can't they?)
Ufortunately, we can't have Saya no Uta on the relations, but since the Sonico Magica April Fool's joke, you can at least have Saya on the relations list. She's pretty much a moe anthropomorphism of pure mindfuck.
Warning. Saya no Uta spoilers ahead!
She is even capable of literally mindfucking people after learning about the human brain.
Since we have the original and Zoku Sayanara Zetsubou Sensei, doesn't it follow that Goku Sayonara Zetsubou Sensei, Zan Sayonara Zetsubou Sensei and Zan Sayonara Zetsubou Sensei Bangaichi should be added to anime relations? If nothing else the opening credits are mindfuck with music.