Yagi wanted an epic death to one of his most fan-popular characters, as this is Claymore, RAWR!
Miria who, after killing her own beloved (Awakened) Hilda, VOWED revenge on the Organization but even more intently VOWED to do her very best and at spending the rest of her life, helping, protecting, and saving her fellow Claymores, would so brilliantly by Yagi, get ironically hacked into pieces by her very own fellow Claymores, that she had worked so hard for and cared so much about, in protecting and helping them stay alive. How cruel ironic of Yagi! How epic and brilliant a death scene by Yagi! What an author/writer/story teller Yagi is! WOW! :D