Board Thread:Theories/@comment-30785465-20170613200126/@comment-32443384-20180202025721

well humans were injected with the beast titan shifters fluid and were turned into somewhat abnormal titans. I would imagine that humans injected with the armored titans spinal fluid would not have the armor ability... but perhaps a human injected with the armored titans spinal fluid would become a normal or abnormal titan, and then injecting that titan again with the serum could grant it some hardening abilities despite it still being otherwise a normal or abnormal titan.

a shifter like eren injected with the armored titans spinal fluid likely gives it the some hardening abilities like annie had. a shifter being injected with a normal or abnormal titans spinal fluid would likely do nothing, in my mind.