User blog comment:B214/Talk About What You Want! 3/@comment-24098614-20141231111340/@comment-16281343-20141231112326

Reincarnated Devils do not lose the weaknesses from their former state.

Loss of excessive blood can be seen as a weakness for Humans and wasn't lost when they were reincarnated.

Another example of a reincarnated Devil that retains their weakness is Gasper. You can also argue in Tannin's case where he is still susceptible to Dragon Slayers.