In Kore wa Zombie Desu ka? season 1 episode 11, there's a song playing at 11:24 and ends at roughly 12:26 (YouTube video by Funimation, region-locked for North America).
What is the name of the song?
The song playing is OST piece 19 called "Yami no chikara"
This song were included in the the second released OST set with specials by Shinji Kakijima whom composed all the songs through out the kore-wa-zombie-desu-ka series