The Good Girl and her Gun

"Im gone but I'll come back."

Story about a teenage girl who was known to be dead from a plane crash. In reality, it was only fake rumors made up by the principal of the school which forcibly made her do home schooling by her parents. As a born assassin, she came back to her old school 2 years after because she was ordered to kill the murderer that murdered a lot of students at her old school which happens to be her boy "Friend". They have known themselves since the third grade but they are to be considered as rivals.

Once they knew each other's purpose, they never had the intention to kill each other. Instead, their feelings grew into a somewhat way where they were inseparable. Even though they knew that they were foes, they never abandoned the feeling they felt for each other. And so, they kept it their secret, the girl pretending that the culprit kept getting away even though it would destroy her reputation as an assassin.

But someone knew it all.
So one of them had to die.

If not, they will receive eternal sufferings in their lives that they can never accept.

-----

Will they escape the barrier that blocked their mutual feelings for each other?
OR
Will one of them give eternal slumber to the person they were inseparable to?