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"For such beings… the only thing you can do is slay them for good," said Abe no Seimei. "Because to them, their very existence is suffering. You'll be giving him a favor, if anything. Okay, and I know what can work for you in regard to that."
"Really?" I asked.
"Yes, but tell me what else he does," he said.
"He can control Demonic Souls…" I said. "He's a full demonic warlock. He has probably also turned his own body into that of a monster… And I suppose he can unleash the power of Hell and Demons."
"I understand now," he nodded. "Very well… Then for such a monster, we must create an ultimate counter ability, I'll make you his nemesis, the very opposite of his existence. You will be his greatest foe and weakness."
He quickly selected several spells after thinking it over and nodded.