I definitely agree with Renoard; this submission is your best yet! The flashback was suitably intense, and the writing seemed a caliber above what we've seen before from you. Fantastic work, I loved reading it!
You take a number of risks with this chapter which had me initially skeptical, but you made it work far better than I expected, so much so that I can't envision it any other way. What I mean is that normally, I'm not a huge fan of flashbacks. A lot of times they can be more cheesy than anything, but this worked fantastically.
Also, when Kail said that Kajsa was pretty, that made me roll my eyes, too. Maybe it was because Ellie found Sicko sort of dreamy that Kail's thought there seemed ridiculous at the time. However. I soon realized how important it was, and I absolutely loved the Kail/Kajsa dynamic (side note: If your viewpoint was third-person limited, having two names both start with a "K" might be a detriment. Having it in first person is a clever solution). The inter-character conflict made this chapter extremely entertaining to read.
Since I did this for the previous Sword of Worlds chapters, so I guess I will point out lines I particularly liked:
Okay, being angry with her was no longer an issue.
I think it was in part because Kajsa had paid no notice to the fact that I was nude, I never saw one flicker or glace from her that showed the slightest interest in my lack of clothing.
“My name is Kail, and you carried me,” I answered her, and she glared at me. I just grinned back at her.
She gave me a dirty look, “I think you know what I mean.”
I'm not sure "dirty" gives the right connotation, given the fact that Kail is obviously attracted to her. Maybe "dark"? (This wasn't a funny line, I just thought I'd mention it.)
I rolled my eyes at her, “Give me a break; I was kinda dying at the time.”
“I’ll break anything you’d like,” she told me with another dirty look.
-Still not sure if dirty is the word you want, but I love the line regardless
Now I can see what you mean when you were talking about needing to refine your magic system. I definitely liked how it turned out. As a physics guy, I really liked the two different methods of gaining invisibility. However, I'm not certain that bending light around you would make seeing any easier. In order to see when you're invisible, you'd have to let a small amount of light (the rays that are about to enter your eyes)
not wrap around you (or go through you, as it is), so your eyes could absorb and perceive the images. At first, I bought your explanation that wrapping the light around you would make it easier to see (because the other method would rule it out immediately, for certain), but on further analysis, I don't see how any actual invisibility would also allow you to see.
Still, your magic system is looking very flexible, and I'm liking it.
I really don't have any major qualms with it. I can't even think of any more minor qualms. The descriptions seemed just about perfect--not TOO wordy, but enough detail. The pacing feels more comfortable, which is great. I actually liked the pacing of the introductory chapters, so I was worried the slower pace post-Portal would kill the book. I am extremely happy to report that it did not.
Simply put: if you can keep writing such great chapters, you're better writer than me!