Responses
Spoilers:
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yup! J turned back time using the watch the system gave him in World 1 because Sayoung died. Then in world 2 Sayoung had the watch patched up enough to use it a second time when J died this time. The reason that people remember world 2 better than world 1 is because the reset of world 1 was better than the reset of world 2. (The watch is only meant to be used once) This is also why World 2 is trying to merge with World 3.
EXPLANATION (maybe ??) :
World 1 : ML die so MC go back in time to save everyone
World 2 : This time MC die and somehow ML turn back time
World 3 : MC is blocked in world 2 in the rift (I think ?? Honestly didn't get that part well) and go back to his current world (3). This is their last chance to save the wolrd