My friend recently played through a game called Persona 4, and he took plenty of screen shots. He showed me this one containing
I understood it as
死 + す, a literary alternative to
死ぬ. I have to admit, though, it doesn't sound very literary to me in this context. 完二 is a tough guy, and he uses lots of verbal forms like
言っとく, so I'm guessing I misunderstood.
To sum up my question, I'm wondering why it was appropriate to say