While Franmalth attempts to absorb Natsu and Lucy's souls, Mirajane discovers the secret to the demons' immortality in Hell's Core, right before Seilah unleashes the restraints on her own power to take on Mira.
As long as we've got the lab, we can be reborn 
endlessly. We're functionally immortal!
!طالما نملك المُختبر، فيمكن إعادة إحيائنا إلى ما لا نهاية، نحن خالدون عمليًا