is there like any context for this? or is this like a metal gear solid moment where its just dissociative disorder

In this future, there's this valuable mineral called Originium, which infect people with a disease... these girls have it, but thanks to it they can also fight. Lappland apparently has a lot more of it than most though, which makes her ... let's say psychologically unstable... the disease has a 100% mortality rate...

The last two pages probably depict a mercy-killing.

It's not in the future, Terra is a whole parallel world, the story takes place in the year 1094 and both lappland's and texas family were destroyed. Her obsession with texas isn't all that natural, it is mentioned that it came as an effect of her oripathy.
Also it is not a mercy killing per say. Lappland seeks to have a fight with texas, and it's sort of implies she does want to be killed by her