Himizu, Tsumi to Batsu: A Falsified Romance Recommendations
Both are about young males who struggle with the desire to kill those they believe to be bad people. Each series delves into the psychological frameworks of the main characters - Tsumi to Batsu focuses more on the main character's state of mind after his actions, while Himizu places more emphasis on the main character's reasoning for his desire to kill someone. The main characters are very similar in that they seem to be psychologically-troubled youths who struggle with loneliness and morality.
Both MCs are adolescent males who believe that despise almost all of humanity. Both manga deal with what happens to a person's psyche after committing murder.