I couldn't help myself but posting several.
Manga quotes, Guts, Berserk.
"He appeared right in front of me, and he wasn't a demon... but what looked like a human. As if he'd been yanked from before into the present unchanged. I gazed at him and for a second... I forgot to kill him"
"A beast, a monster? Heh... Don't make me laugh. I... am me. And nothing on earth. Can change me. No matter who chases me."
Anime quotes
"No matter how strong, for a human to fight a monster means he has submerged his humanity and transformed himself into a greater monster." (Schierke, Berserk)
"Stop Whining! All I did was cut off your stupid legs! Summon your demons! Transform yourself! Regenerate your legs! Stand up! Pick up your gun and attack me! Do something! The night is still so young, and the real fun is yet to start! Hurry, hurry, hurry, HURRY!!!"
(Alucard, Hellsing)
"To become a monster like me, is to admit you were too weak to remain a human." (Alucard, Hellsing)