User blog comment:BlackWizardZeref/Fairy Tail: Chapter 380 Hell's Core/@comment-76.124.155.27-20140413200702/@comment-24546844-20140414190053

Err... I don't know. I like the number 100 more than 80 I guess, and also to Freed's runes 81=100=999 as you said, the rules only state "80+ can't pass". The point is if this theory is right, than Natsu's magic would be above 400 years making him a valid target.