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Kanone Hilbert (カノン・ヒルベルト)A Blade Child with a dual personality. He could be cute and friendly or manipulative and insane. He was very close to Eyes. He would cry for Eyes when Eyes could not when they were young, but their friendship fell apart as they grew older and developed vastly different opinions on the fate of the Blade Children. Kanone will go as far as he can to kill the people who give the Blade Children false hope, to prove to Eyes and the Blade Children they have no hope. He is capable of terrible things and is interested in killing Ayumu because he is the Blade Children's only hope that they can actually be saved. Kanone is even willing to work with the Hunters to prove to the Blade Children that they have no hope.
It is also stated that he learnt the art of killing at a young age. in chapter 35 he also said he could kill all the students in the cafeteria in less than 20 seconds.
(Main Source: Wikipedia)
Other sources: Manga chapter 35 page 21)