How about this synopsis of the ending, TEAR is the last remnent of emotion in the world, being the embodiment of Hiroko's emotions. And the, shall we just call it, child of Kiyoko and Novem, kills her to ensure no emotional 'polutants' for the future world. Even though she was born of love, at least from Novem's side, it would make her more like the irony. She being born of emotion, but destroying emotion all together. The only problem I see with that is, she does show a form of emotion at the end, she's pleased, if not looking a bit insane, at the murder of TEAR.