It's explained later when Ryuu goes back into the dungeon after she is healed. It dead turning to ash. It's what finally broke her. All her friends' lives, and magic did NOTHING. Their sacrifices were meaningless in her mind.

Juggernauts lack magic stones, but they have timeline and or damage limits. Once the 'virus' on that floor has been destroyed and it hits the timeline it turns to ash.

@StinkyPete12

What Ryuu was made about wasn't because her friends attacks barely damaged it, but rather because she wanted to avenge them but was unable to since the Juggernaut had already died.

We are also told that because of it she decided to shift her anger towards the Rudra Familia. Ryuu simply wanted to unload her rage into something or someone.

You are right that the Juggernaut has a time limit, but it won't strictly disappear once the threat is eliminated, but actually when it reaches its time limit.

Did they mention or anyone can make a rough estimate of how long the time limit is?

It’s been a long time since I read v14, but the Jugernaut was basically like the dungeon’s security system. I thought the first time after it killed Astrea familia it just ceased to exist on its own, because it determined that it eliminated the threat to the dungeon.

Again it’s been a long time since I read the volume so I might be wrong so if someone could confirm this to me I would be grateful. @Angelo Gabrini is this right?

Yeah that's what I remember happening too. The Juggernaut disappeared on its own after all the threats were removed, basically just acting like an antibody.

The reason it was a problem during v14 was because the villain used his ability to try and "tame" it to target Ryuu and Bell, so it would keep going until it or them were eliminated.

What happened with the Juggernaut that killed the Astraea Familia is that it escaped after being hit by Ryuu's magic. Alise had been able to destroy its magic reflecting armor by sacrificing herself and Ryuu used said opportunity to land Luminous Wind, which dealt massive damage to it.

Jura may have hid himself but if the Juggernaut really only disappeared until the threat was eliminated it would have only done so after re encountering Ryuu, as it obviously knew she was still alive.

@InversePrime

The Juggernaut didn't follow Bell and Ryuu because of Jura's orders actually. What did happen is that the collar prevented it from hearing the dungeon's voice and therefore allowing it to act based on its own free will.

And the Juggernaut, acknowledging itself simply as a killing machine, was angry at Bell for getting back up, fighting and ultimately surviving against it. Basically, the Juggernaut only went after Bell out of an injured pride. It didn't really care about Ryuu until the final fight, in which it finally viewed her as someone also worth killing.

That's true, because of what Jura did, the Juggernaut was broken free from its original purpose, which is why it was able to go on its rampage.

The original Juggernaut at least I know wasn't actually defeated by the Astrea Familia, only injured, which is why it seems like it let itself dissipate after its "purpose" was resolved and no longer sensing any threats to the dungeon.

From the fact that the dungeon kept instigating the Juggernaut to go back to the Water City in spite of the only ones remaining being the Hestia Familia expedition group it is obvious it isn't the Juggernaut itself who decides when its mission is done but the dungeon, and that it doesn't consider it has finished until literally everyone has been killed.

So the one who killed the Astraea Familia vanished from the time limit rather than because of feeling its purpose had been fulfilled. Juggernauts were never said to be able to vanish out of their own will so I don't understand were you are coming from with that.