Board Thread:Questions and answers/@comment-30069821-20161031231921/@comment-8695373-20161102191500

Oh, I see what you mean about Naoto. Basically, he died, but Raquel bit him, sharing her own life with him, so he lives as long as she lives. She also made him a new right arm from her blood (since he lost his own), and that blood kinda merged with his blood, making him stronger, but I don't think his lifespan is affected.

Ragna's lifespan did change because of the Azure Grimoire, but it became shorter, since the Grimoire was slowly corrupting his body.

And, Nu was described as a girl that looks like she's around 15 years old, so maybe she looks younger than Noel.