Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
Speculation why Witch Killers got their power.
- Yamada got the copy power because he wanted to be like Ushio, to be able to have a friend.
- Tamaki and Ushio got the cut&paste power because they were jealous of everyone of loneliness and want to take over their identity.
Ushio and Odagiri were not dating in the past.
It's been mentioned to Ushio by Yuri that Himekawa told him that the two were dating in the past before their memories were erased several times, but the thing is that while memories can be erased the emotions one feels can not. Such as Shiraishi feeling sad when she saw Yamada and Odagiri kissing yet not knowing why. Odagiri has never shown such a situation with Ushio, while he's always been in love with her even after his memories are erased.- Confirmed. Odagiri was in love with Yamada all along, and Yuri is shown to have been manipulating Ushio.
Hikaru's power
Hikaru's power will be similar to the Body Swapping Power.- Jossed. It was the charm power.
Witch Killer Powers...
...were born in the school to counterbalance the Witch Powers.The person who erased yamada's memories
we know that Yamada memories has been erase by both of the 7 witches in his 1st year of highschool but Rika has never commented or reference she did it to him even after they became friends and she was busy with Leona and Yamazaki. also in the flashback arc the Presidentess gave someone (we did not get to see) the order to deal with yamada group, so unless there a 3rd batch of witches the mysteries person who dealt with yamada group was a witch killer who gained Rika power but it can't be the steal power so it either have to be a new power or the copy power. also if the person is in the same year as Yamada then they would still be at the school. tamaki and ushio showed that two witch killers can have the same power at the same time, so both can have the copy power.Alex's power
Seeing now that a set doesn't have to have one of each power types, Alex might have a Mentality power. If not then his power is a Precognition power.- Jossed: His power is the body swapping power
The True Akashic Recorder
Although the Ushio suspects The chairperson to be the Akashic recorder, she can't be the one who wrote the Witch notes. First she was not part of the Supernatural Studies Club during her first year as Leona and Haruma were only ever seen in the room, prior to Rika joining them. The Witch Notes were stated to have information on the witches atleast several years before Yamada's first year, meaning there is was someone else who had been the Akashic Recorder at that time who made the Witch Notes with the SSC at that time.