[larethian]

Originally Posted by Xacual

Spoiler for The Killer:

She kills people and takes their souls and uses them like extra lives for herself. That's another reason she was confused about Ayumu because she didn't get her extra life as it were. It has been causing problems for the Underworld because people are dying but no souls are at the murder sites to be collected.

Link is a translation to chapter 3 in volume 1 where it's somewhat mixed around from the anime. It seems like Ayumu confronted Yuu about the murder thing at the end of chapter 2 and Sera took the two to the bowling alley to try to cheer up Yuu. Which is where Ayumu and Orito ran into them. Massively cute Yuu moment in this too. Also includes Ayumu talking to DaiSensei about Haruna and Yuu explaining her powers to Ayumu. Also explanation of what Megalos are.
http://pastebin.com/Gu3K8Bv4

I read the Japanese wiki regarding Kyouko.

Spoiler for Kyouko:

It says that Kyouko is serving the King of Night, and she was killing and capturing the souls to offer to him, though in doing she gains a level of power rivaling his. In her fight with Ayumu, she lost her ability to transform into Masou Shoujo. And later it was divulged that she knew of the past of the King of Night, and wants to save him.

Of course, the wiki could be wrong.