Basically, travelers are people who get Isekai'd in a certain world, live a life there, and the moment they die, they get sent back here in this space again and... repeat the cycle. An additional piece of information is that Travelers also lose their memory of being a Traveler specifically after they get Isekai'd. Travelers only realized that they were a Traveler all along after they went back here, just like what's happening to Yuki right now.
Jujutsu Kaisen: The Traveller
Anime & Comics · Evrabonzz
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