In the Sword Art Online anime, after getting the Resurrection Item Kirito gives it to Klein, as Kirito wanted it to bring Sachi back to life, but for it to work it had to be administered within 10 seconds.
Do they ever explain what happened to the item after that; the anime doesn't show if Klein ever used it or not?
This item was not mentioned after it's introduction.
During that introduction Klein was given it with the instruction to use it on the next teammate who dies in front of him.
During the final battle he has every motivation and opportunity to use it as the wife of the man who gave it to him has died right in front of him! He does not use it here. It is unreasonable to think he would not use it under that circumstance.
An object like that would not be disposed of carelessly.
This yields two possible answers: he followed the instructions given to him (Very possible) or he gave/sold it to someone else and they used it, sold it again, or retained it until it did not matter anymore.
In either case, this is neither a plot hole nor a deep mystery as it was a relatively minor plot element, we were told exactly how he should use this consummable, and, if he did so properly, it would not have been a large enough plot point to warrent it being shown. I doubt it would retain its value by the later stories so it doesn't even matter if it wasn't used by a purchaser by the end of SAO.
After giving the item to Klein, it's never explained what became of the item. The reason for this is because of the way SAO was written. I would go into details, but I'll try to make it simple.
SAO was originally a Web Novel, written from 2002 to 2008, before the author was asked to publish it in 2009. Most of the side-stories that took place in the "Aincrad Arc", were written around 2002-2004 (After the first "Volume" was already written), between the other major arc, Fairy Dance and Phantom Bullet. "Red Nosed-Reindeer" (the story that Episode 3 is adapted from) is different. Kawahara didn't write this story until after 2005, when he had already began writing the final arc of SAO (which isn't even in the anime yet)
Effectively, when he first wrote SAO, the Stone was not a concept he had in mind. When he began publishing, he never bothered to write the stone into any other story either (even though he included "Red-Nosed Reindeer" as a side-story in the second book)
I would have to assume that the stone was used to save one of Klein's Guildmates, considering that in the novel it was said that his Guild never suffered a single casualty.
In my opinion, that stone was something that could have been brought back in a major way. A previous poster mentioned the stone would have been perfect to resurrect Kirito in that final battle, but his will to overcome the system after witnessing his true love fall for him would've been less meaningful to the whole story, and stories ahead. Or it could have been used in any of the floors skipped in the amine. To me I it just seems like Klein followed Kirito's instructions and just used it on the next person he saw die; which was probably a lot considering the rate of deaths that likely would have happened in his presence. This is this only thing to go off based on actual fact of the Anime.
I've never read the light novels, because I wonder if they have more content from the floors that they majorly skipped in the show.
