Just a funny post I found on tumblr, actually kind of a solid reason so I thought I'd post it here. This applies specifically to the Pretty Cure series so if u like that toon as well!
When a human is marked to die, a faint gray line that is invisible to most appears around their neck. As time passes, that ring becomes darker and darker, until they die
Yakumo's Sealed Power Naruto Season 4 : Ep. 204|23:39| View beschrijving Naruto has a dream about Yakumo wishing to become a ninja and Kurenai threatens to zeehond, seal her power Hide beschrijving