At risk of completely outing myself as an old fogey, I intentionally left that phrasing in when I was doing my edit/QC because it seemed to fit how teenagers speak, and I still struggle with trying to keep my own verbal tendencies as a decidedly not-teenage person from blurring that. I can't speak for everyone else though.
Alright~
On a side note, I notice that speech tends to end with the comma outside of the quotation marks. For example on pg 9's < “Wouldn’t have thought”, Adachi replied, > shouldn't the comma be within the quotation marks like < “Wouldn’t have thought,” Adachi replied, >?
Also from your post on the 1st page, it seems like the above example should have been "Wouldn't have thought that".
(I apologise if it seems like I'm nitpicking.)