Leveling Murder is a Manga/Manhwa/Manhua in english language, GORE series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

One day, Onitsuka Yamato, an office worker, kills another man who attacked him. When he took that man's life, a sound effect rang in his head informing him of his own strengthening and the acquisition of a spell.
He had become a "murdelizer", a being whose level goes up when he kills someone.
Yamato resolves to survive - even if it means killing people, kill someone within a week or else he will die.