That doesn't make sense. His sister was a citizen, a victor of a previous Borderlands incident that chose to remain there. She would have already died previously, not in the meteor incident.
I hate these kind of endings regardless of whether they survive. It doesn't make sense why Yuu wouldn't be there for Masaki's fight, or his girlfriend for that matter.
I've found when a manga exposition dumps you can almost always skip most of it and things will still make sense. The characters doing all the thinking tend to be inconsequential in the long run and just an opportunity for the author to wank off his planning.
TL;DR: I ain't reading alla that shit
Imagine if one of them was secretly a paranoid schizophrenic and was trying to convince themselves the commuters watching them were just the disease because there's no way they're getting gangstalked.