User blog comment:Real Godisme/Chapter 481/@comment-3423279-20160411185350/@comment-7418318-20160411223729

But Iced Shell doesn't just use magic, it converts the life-force of the caster. Even Neinhart calls them "Historia Corpses", which would strongly imply they have no life-force, since they are corpses or something similar to corpses.

As for the Naruto example, that's irrelevant since it's another series with different rules.