I think Lady Mikage wants to get rid of Honaka to prevent the higher ups from nuking them all.
She knows about Kazane's and Honaka's bond, she was coerced into erasing the memories, and most likely knows the seals are breaking.
By getting rid Kasami who also has the Chair Woman's blood, and Natsumi who was created for Honaka, also she is closing all the loose ends. Poor Tanpopo and Yoshiko were just in the wrong place at the wrong time.
She first off kidnapped her brother and threatened her daughter, who is obsessed with him, with his death if she didn't do as she asked. Then gave Natsumi the spell to create the world to trap them to Kasami who is obsessed with her brother. Kasami then made the world and Lady Mikage then collapsed it her self to get rid of all evidence. But Natsumi is pitting Honaka against her, and hopes the necklace she gave him gives him enough power to beat her and save them all.
It can't have been a Tower Witch cause they want his body and easing him wouldn't serve their purpose.
Final note she is probably going to kill Mikage Sensei and make it look like a Tower Witch did it.
Edited by Coppercredit, 12 April 2015 - 01:58 AM.