Man I'm gonna have to update this shit when I reread Negima proper. Anyways the primary thesis of Negima, above even the whole "shit's fucked but you have to keep going," is thus: What makes a person?
I mean that in two ways: the first one is the philosophical one. What is a person? How do you define a person? Is it a human? What of Evangeline, then, who is a monster but was born human? What of Chachamaru, who is not even made of flesh? What of demons, youkais, ghosts? Where do you draw the line between what is a person and what isn't? What of Asuna? She's a copy, a fake personality crafted to protect the real one. Is she a person? What of Fate? He's a homunculus, a machine, he's man-made. Is he a person? What of this lady who kins Asuna? During that brief moment, she truly believed she was Asuna. Does that make her a fake? She's not the original, but is she a person?
The second way is more ethical: what, and who, decides when someone deserves to be treated like a person?
Evangeline is not a human, that is established. But further than that- she is evil. She killed people without remorse and make it very clear that she would do it again. Can she be treated as a person? Isn't it so much safer, so much more convenient to stick her in a box labelled "monster" and bask in the idea that ah, yes, we would never be like that? And even aside from all of that- Evangeline is stuck with the body of a child, ie a category of people whose basic agency is frequently denied. Is she a person? Can you see her as someone with her own wishes, mistakes, responsabilities, thoughts, even if she barely looks a day over eleven.
What about demons? The first time we hear of them, it's through Negi's backstory- demons swiped in and destroyed his village. They show up again as summons in the Kyoto arc, and through the manga in general as mooks to beat up. Are they people? It would be so easy to write them off as a mindless evil horde. Yet in the Kyoto arc, they banter with the fighters, telling Kaede & Ku they'd like to fight again one day. Graf Wilhelm Josef Von Herrman shows up with his own hobbies & agenda, and even something akin to a sense of honor. The demons we later meet in the Mundus Magicus are all Just Some Dudes- often antagonists, often perverted, but no more than any other character in the manga. Are they people?
Setsuna's entire arc is about struggling with that question. She's not human. All she knows is how to fight. Yet, to find love & happiness, she needs to be a person. Can she do that? Can she be a person while being a monster, a killer, a half-demon? Evangeline & Tsukuyomi both doubt it. Evangeline has long grown used to being unpersoned & deshumanized. Tsukuyomi meanwhile doesn't think of herself as a person at all- she's a blade, thirsty for blood and uncaring of anything else.
That question culminates with the Mundus Magicus arc, where it's revealed that natives of the magic world will disappear when the magic of the place runs out. Kurt Godel refers to them as "illusions"; he certainly doesn't see them as real people in any capacity. What of you? What do you think of them? They're made of magic instead of flesh. They laugh like you. They cry like you. They bleed like you. They have cat ears and horns and fangs. Is that a person? Answer me. Is that a person?
Negi's answer isn't just of course they're people. His answer is that if there is such a divide between a person an unperson, then this divide should be destroyed. When he forms a pactio with Chachamaru (a magic ritual which require both parties to have a soul, something Chachamaru fears she lacks as a robot) his initial thought is "I will prove that you have a soul," followed by "actually it doesn't fucking matter if she doesn't have a soul, this is my friend I know she's real I know she's a person and no one gets to tell me she isn't." Nothing, no one should have the authority to just decide who deserves respect and who doesn't, who deserves to live and who doesn't.