Wow, what an action-packed episode! Lots to unpack here.
There’s a general feeling of unrest and suppressed tension starting to emerge amongst the people of Island. Rinne finds a wanted poster of Karen, and although Karen tries to take Sara hostage so she can enter the church and find the other children, Sara persuades Karen to let her help lead them to the untagged children. Rinne will stay behind to guide the mystery machine she’s been building.
Sara, Karen and Setsuna sneak into the church but are found by a disciple named Mei (one of Karen’s high school friends on Urashima. Mei tells them that the untagged children are in an underground warehouse. However she neglects to tell Sara that the children are all dead, and that armed guards have the body site set up as a trap. Mei pays for that negligence with her life.
Sara, Setsuna and Karen are marched outside the church where they hear Sara’s father giving a speech from a church balcony to the people of Island. Suddenly he is assassinated and falls from the balcony to the ground below. Sara is allowed to rush to his side, with Karen and Setsuna following close behind her. Alas this too is another trap, one which results in Sara, Karen and Setsuna being framed as terrorists. The people of Island work themselves into a frenzy over this unexpected death and call our trio witches to be burned at the stake.
However Rinne appears at the last moment (disguised in an oversized robe) and urges the public to run away because supposedly the terrorists are coming with more bombs. To prove her point Rinne has rigged fireworks to explode as makeshift “bombs”, figuring that the residents won’t know that they’re harmless. Sure enough the public flees, allowing Rinne to put water on the fire burning at Sara, Karen and Setsuna’s feet. However after their rescue Sara collapses from an injury she acquired on her leg during the fight with the armed guards in the warehouse.
Rinne leads their group outside Island, where Sara asks Setsuna to put her down. She takes one last look at Island and with her dying breath asks Rinne and the others not to hold a grudge against the people of Island. Well. Turns out her leg injury was more serious than Setsuna thought.
Setsuna and the girls bury Sara, and then Rinne continues to leadKaren and Setsuna towards a mysterious cave which supposedly holds relics of an ancient technology. Wait a minute, is this…? Could it be? Yes it’s the cave from Boryujima! Setsuna touches a panel on the wall that causes the entire room to light up, and Rinne becomes one very excited researcher. There is enough rations to last their group for two weeks, so Karen and Setsuna spend that time putzing around the cave and outside surroundings while Rinne does her research on the gigantic computer filling much of the room.
However during this time it becomes clear that Karen is very, very sick. Without even knowing how he knows, Setsuna diagnoses Karen as having soot blight syndrome. Her symptoms didn’t appear until they left Island because the disease only activates once its victim is exposed to natural sunlight, which Karen wasn’t until they left Island.
Faced with no other choice, and with Rinne having reached the limit of what she could research from the cave, Setsuna and the girls return to Island to take Karen to a 
doctor. I was mildly annoyed to see Setsuna walking ever to slowly through Island with Karen on his back. Isn’t her situation a little more urgent?? Setsuna finally does reach a hospital only to learn that Karen died while he was carrying her on his back. ;~;
Setsuna and Rinne return to Rinne’s room, and with the addition of all her new research, she’s learned that the machine she’s been building with her family’s blueprints and old research paper was a time machine! Now they can use this machine to travel back and save Sara and Karen from dying!
Except Setsuna suddenly has flashbacks of his time on the original Island. He remembers Karen, the first Rinne, and many other memories. Suddenly everything is clear – he came to this future to save the first Rinne. If he travels that far back, then by proxy this new Sara and Karen will be saved too. Or will they? Rinne points out that if Setsuna travels to the distant past to save that Rinne, the future Island they are in presently might not come to be. Therefore the second Rinne, Karen and Sara may not even come to exist at all.
It’s a sobering though, but Rinne loves Setsuna enough to let him travel to the far past so he can save his first love, the first Rinne. Even if the second Rinne’s history never comes to exist as a result of the butterfly effect.
During the credits Setsuna and Rinne make their final preparations. Rinne works on the time machine while Setsuna works to make him and Rinne a pair of wedding rings. They tell each other that they love each other, and Rinne says she wants to have a quick wedding before Setsuna leaves.
As the episode closes out, Setsuna promises to remember Rinne. Setsuna then climbs into the time machine and Rinne starts it up. Rinne sets the time period Setsuna is to travel into the past – 20,000 years!! Wow! (But if you think about it, if the cave on Boryujima is now surrounded by snow and ice, it makes sense that a lot of times has passed. I just didn’t think it was quite that much. ^^;; ) (How does Rinne know that that’s how far back into the past Setsuna has to travel?)
The title for the next episode really has me curious – “We’ve Met Again, But You…” Whose POV is it from? Does Setsuna change somehow when he travels back to the past? Is Rinne somehow different than before she died? I’m honestly curious about whether the Island Setsuna just left, the one set 20,000 years in the future, is the one he left in the first place before he washed up on Urashima. Regardless we have only 2 episodes left and there are still a few mysteries left to be solved so I’m very excited for this series’ finale! 😀