Tobirama to Hashirama Honorific Question.

[Eishi]

Dear Hipster, it's "anija", an old expression of "older brother"

兄者

He uses "Kisama" with Hiruzen and Obito. "Kisama" is also an old expression of "you" used by the upper class

But he uses "omae" with Minato and Naruto which is less formal but friendlier.