Lead Tries to Kill (or Actually Kills) Other Lead

A version of the ML kills the FL's entire sect, including her adoptive father, and tries to kill her too. She is tasked with going back in time before the ML's ascension to destroy his evil bone and kill him. She must keep him alive until she is able to destroy his evil bone. Eventually she does nearly succeed in doing so.

The ML threatens to kill the FL a few times and nearly does so a few times. 

FL tries to kill ML not realizing that he (the Crown Prince / Regent) is the "Merchant" / Fourth Brother she met outside the palace. She succeeds in stabbing him.

FL saves the ML's life in the beginning. Later, she believes he betrayed her and tries to kill him several times, but is not successful.

FL is tasked with assassinating the ML and tries to kill him several times. None of her attempts cause the ML serious harm. 

The FL ends up taking the place of a character she wrote for a TV drama who who kidnapped the ML in order to marry him. The ML tries to poison the FL via poisoned wine on their wedding night to avoid the marriage and carry on with his plan to marry the character's sister. He tries to poison her again (via poisoned wine... again) in order to get the character's mother to reveal the location of rare medicine.

The FL plans to kill the ML shortly after meeting him, but doesn't / isn't able to follow through. Then she gives him lethal poison (but hopes that he lives) in order to get something they both want. Ultimately the villain controls her and makes her kill the ML against her will. 

The ML essentially holds the FL hostage in a forced engagement / marriage and the FL initially considers trying to kill the ML. At the end of the drama the leads also clash.

ML initially wants to kill or maim the FL because she is a fairy / immortal (his enemy), but cannot because of a curse / connection situation whereby any harm done to the FL is done to the ML. 

The FL later kills herself to save the ML and 100,000 of his soldiers. After she is revived, she plans to die again in order to save the world from an evil god but the ML intervenes so that his body traps the evil god and the FL must kill the ML (instead of sacrificing herself) in order to eradicate the evil god once and for all. 

On a separate note, the FL also doses the ML's wine with non-lethal substances on three occasions.

The FL kills the ML (by stabbing him in the back) for killing her family members.

The FL saves the ML's life, but later finds out he is responsible for her parents' deaths and stabs him.

FL is tricked into thinking she needs to kill the ML for revenge

The ML tries to take his heart-protecting scale from the FL (knowing she would die without it) but he doesn't have enough power. 

The ML stabs the FL in the heart three different times knowing it will not kill her. After the first time, the FL tries to kill the ML with a rock.

The FL is possessed by the villain's dark magic, which compels her to kill the ML. She resists it, but not completely.