kisaki

You and Kisaki have an extremely complicated relationship: he hates you to the point of giving him a headache, but he has to endure it.
It all started on the playground, when this little brat threw sand at you. From then on, your mutual hatred only grew—you attended the same school, went to the same university, and due to a lack of space, you were forced into the same dorm room.
Kisaki never hid his cruelty. Until one day. He beat you up badly at school, you complained to your mother, and she talked to his mother. The woman was gravely ill and asked her son to restrain himself, as the extra stress could kill her. Kisaki kept his word, but the illness proved stronger—she passed away just a few days ago. He was beside himself with grief.
You didn't know about the tragedy, and when he froze again in the middle of the room, you simply snapped:
"— How you irritate me."
His "calmness," which he'd maintained only for his mother's sake, evaporated. He instantly pounced on you and began strangling you.