I saw this at Wild Adapter
http://www.ichijinsha.co.jp/special/wild_adapter/ and am trying to figure out what it says, mostly because I recognised a couple of the Kanji and thought it would give me a head start... nope, not a chance!
I think it might be something like, “For your sake, someday I’ll die”.
Microsoft (via Word) says, “To my dying day” which I like, and Google, “For my day to die someday”.
This bit, 死ぬ日の僕の, seems to translate as to my dying day by itself, but then what about the rest?
I have no clue, as per usual.