The user can control their killing intention and use it to intimidate others, it can be used in two ways:
The user can give off their pure killing intent, affecting opponents, themselves, and others around the vicinity. Particularly strong killing intent can paralyze the victim in fear, causing them to morbidly hallucinate their own deaths, or even kill them by forcing the mind to believe their death is reality.
Suppression and Perception
If the user has mastered control over their emotions, they can control their killing intent by suppressing it, to prevent their opposition from discovering it, thus hiding one's motives and preventing one from being tracked by such emotions.
Anyone who can also perceive a foe's killing intent can perceive the foe's next move and prepare the next appropriate move in advance.
Apathy: by suppressing the intent while retaining desire to kill.
Akame (Akame Ga Kill!) suppressing her killing intent while fighting Zank the Beheader to prevent him from reading her movements.
Nagisa Shiota (Assassination Classroom) possesses incredibly potent natural instincts for assassination that allow him to completely suppress his killing intent to the point that not even highly trained assassins or veteran soldiers can detect it or…
…emit pure killing intent so fierce it incapacitates even experienced killers and…
…years of living with his deranged mother and having to endure her mental abuse and anticipate when her psychotic outbursts would occur has made him highly perceptive to the inner thoughts and emotions of others, enabling him to read and gauge their state of mind just by looking at them to determine when or how they are most vulnerable.
Kazuo Kiriyama (Battle Royale) apathetically exuding his killing intent, due to his brain damage sealing his emotions.
Kenpachi Zaraki's (Bleach) killing intent manifesting to the form of his spiritual pressure, making Ichigo hallucinate being stabbed.
Even while smiling serenely, Retsu Unohana, being the first Kenpachi and the most diabolical criminal to have existed within Soul Society, can get people to do what she 'requests' by projecting Killing Intent.