Post a character who often, always, or almost always goes by his/her last name/surname

koichi sakakibara almost always goes by his last name,sakakibara...........

Zura! er... I mean Katsura X3 Kotarou Katsura, not once he was called by his first name in the anime, it's always Zura or Katsura XD

i guess tetsuya kuroko always goes by the his last name kuroko

Kazahaya

Youhei Sunohara from CLANNAD. The only character who ever really addressed him as 'Youhei' was Kyou Fujibayashi, and he had not granted her permission or clarified that he felt comfortable with that.