It's just something like extra HP. Although Ikigaya had a similar ability that seemed to protect.
From a gameplay perspective they won't learn it, but how it looks in terms of RP is secondary.
Well yes, or maybe due to some obsession or specific trait.
Both.
Will Deus's Knights (Alaria, Axel, Lester, and probably Alex's character) be focusing on main solo content or will there be an emphasis on teamplay?