[quote=@Ashifili]
Gae Bolg only ever killed mortals though. Even if, say, it had the conceptual ability to impart death onto all subjects, the problem with Rui-Ling is that his immortality takes the shape of 'automatic resurrection after death'. It's not killing Rui-Ling that's the problem. It's the 'automatic resurrection' that needs to be taken care of somehow, but currently, yea, Lucille's the only one that can keep him dead, and even then, that's only until she tires of lugging his corpse around with her everywhere.

In regards to geis, [url=https://en.wikipedia.org/wiki/Geis]there's a similar problem...[/url]
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Kek, with all the money that Chikage's throwing around, I wonder if someone will eventually just straight up purchase the Dangeki Cosplay Shop. XD
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Then, you would have a similar problem with the Lance of Longinus, 'cause... you know, the spear's most famous kill revived three days after his death, so it's not a useful means of keeping people dead, IMO. Maybe if we look somewhere else, like Greek myths, you cold find your answer. I believe that the bow and arrows that Heracles used to kill the Lernaean Hydra, would be a good starting point for his troubles, since they became infused with the beast's venom and it was a sure kill to whatever is it that got poisoned by the arrows. The old myths are full of creatures that somehow couldn't die, but end up being killed anyway, so at least one solution to Ruri-kun's problem must exist.

Just remember the words of eternal wisdom by a fellow boy that couldn't die so easily:

[center][img]http://i3.kym-cdn.com/entries/icons/original/000/001/593/peopledie.jpg[/img][/center]