Post characters who are reserved and tactful as well as responsible

William T Spears - Black Butler

Shinigami London Division Department Manager
His tact may be questionable at times but for dealing with Grell all these years, he does very well and without question is responsible and reserved.

Isumi Saginomiya from Hayate the Combat Butler. In one episode, it was commented that she didn't really need a butler or a maid because she was responsible. However, she could probably use a servant to help her with a little common sense or prevent her from getting lost.

Levi Ackerman from Attack on Titan

One I can think of would be Kouta from Elfen Lied