John was hungry for Karkat's mutant blood.
The two of them have been together for 3 months and nothing really got in the way of their relationship until now. The vampire boy didn't want to hurt his boyfriend, but his new instincts didn't care. Turning on his cellphone he called the troll. After a few seconds of it ringing he answered.
"HEY."
"Hi."
"SO WHY'D YOU CALL ME?"
"I was wondering if you wanted to come over."
Silence.
"SURE. WHEN?"
"Right now."
"ALRIGHT THEN, I'LL BE THERE IN TEN MINUTES."
Karkat hangs up. The vampire paces around, anxious to sink his teeth into the troll's neck. Ten minutes pass fairly quickly. The doorbell rings, but then John realized that the sun's out. He gets an umbrella and unlocks the door, he quickly returns to the shadows. "Its open!" He hears Karkat open the door and close it. "JOHN? WHERE ARE YOU?"
"In my bedroom!"
Karkat walks into the bedroom and sits by John. "I'M REALLY HAPPY TO SEE YOU." He says sweetly. Then he takes a second to look at John's clothing. "WHAT'S WITH THE NEW CLOTHING?" John took a moment to come up with an answer, and then spoke. "I just felt like wearing something new." Karkat shrugs and gives him a kiss on the cheek. John feels his patience wearing dangerously thin.
After the troll pulls away he lunges after his neck, kissing it at first. Karkat let out protests then purrs, when he let his guard down John sank his teeth into his neck. Karkat howled with pain and cringed, trying to get away from John. But John had his arms wrapped firmly around him, enjoying the mutant's blood. After he finished feeding Karkat looked paler and there were two bite marks in his neck, oozing a little stream of blood.
Karkat got out of John's grasp and walked towards the door, wobbling. Before he could reach it he fell and hit the floor, unconscious.