Spoilers for both seasons of Daredevil below.
In "Speak of the Devil," Daredevil kills Nobu after a brutal duel.
Murdock never talks about this, even when discussing murder with his priest.
LANTOM: That thing... brought you here last time [killing Fisk] ... didn't go so well?
MURDOCK: Not so much.
LANTOM: The man... you talked of... did you...
MURDOCK: No, I didn't kill him. (sighs deeply) But I tried to.
LANTOM: And are you disappointed that you didn't succeed... or maybe a little relieved?
His various discussions with the Punisher seem to imply that he has never killed anyone before.
For example, from "New York's Finest,"
DAREDEVIL: I don't kill anyone.
We later learn that Nobu came back to life, but Murdock did not know that at the time.
While the act was self-defense, and arguably justified, it seems odd that he never mentions it again.
Why did Daredevil forget about or act like Nobu's death never happened? Has there been any Word of God on this?