Deimos had become silent for the moment, understanding quickly that she wanted to explain what it was exactly. His reasoning for not knowing of something such as Mega Evolution was understandable really, considering his own sheltered origins back in the mountains. He had never truly heard of it's existence until now.
He shifted his focus entirely to Nira as she began to explain just what Mega Evolution was. He shook his head at her original question, before listening intently. At first judging from her explanation, he judged it as some form of temporary evolution, which merely served to confuse himself. The Absol species didn't have a regular evolution, thus he didn't fully understand her at first. He understood that it seemed to be a temporary process for use in emergencies however.
He finally caught on however at the last, quiet part she revealed. Not all Pokémon could use them... But beings such as themselves could, seemingly separate from true evolution. This brought one clear question to his mind. He understood it was meant as a gift but if it provided her a means of better protecting herself... Why did she value himself over her own safety. There had to be some reason for that... Something she hadn't revealed, at least that was the gut feeling he had received.
"I... I see. Then allow me to ask you one question. If you wield the ability to, upon evolution, to utilize this ability. Why are you... Giving a means of protecting yourself... To me? Both of us know I dislike seeing you in pain. If this could help you better ensure your own safety, why do you wish me to have it? I understand that it's meant as a gift but... That's the one thing that doesn't add up." The Absol questioned her. He couldn't be there to forever shield her, he knew that well enough. He didn't want to render her complacent, unable to shield herself from harm for this exact reason.