Quote Originally Posted by Calemyr View Post
A World Line is a collection of time lines.
I guess this makes sense. In theory they're just very similar timelines, in practice it would be useful for time travellers to group them all together and give them the label Worldline 2814 or something to distinguish it from the Worldline where Axis powers won WW2.

Quote Originally Posted by Calemyr View Post
Other than that, there's one question I'd add for your list of things to remember: Why is it only Okarin that remembers the first World Line? I remember that really bothered me first time around.
I originally thought that Okarin was the only one to remember the first World Line because he literally travelled from one world line to another, and no one else did. Recently though I've been considering the possibility that he hasn't been travelling, just that something happened that changed the world line and he retained the old memories. One piece of support for this is the texts that Okarin sent about Kurisu's death, which he can't actually find on his phone. So that particular piece of physical evidence from the other World Line is gone.

The thing that distinguishes these two ideas is other physical evidence, like the metal Oopa and more importantly the texts that were sent about it. If the texts are on his phone now, it's time travel, if they aren't, then it's a change in memories. Okarin hasn't mentioned that they were missing, but he might just not have noticed if they were, what with all the other more significant stuff going on.

It's actually a very important distinction, from my perspective at least: If his memory changed instead of him physically going from one worldline to the other, then my current theory on Kurisu's personal timeline is completely wrong. (Well either that or we have a weird situation where Kurisu time travelled while Okarin is just remembering a different timeline).

At this point I'd bet on actually travelling from timeline to timeline instead of just a change in memory, but if it were a change in memory I would guess Okarin was unaffected because of his schizophrenia.