If you haven't read Prince of Darkness, that's where it tells how Adrien became a vampire.
Characters belong to (c) Zagtoon.
6 years ago when I was bitten by bats, I became a vampire and had to leave Paris to go to Transylvania to be with one of them. It was like my undead life lead me to be a new person than a human. Dracula, the legendary prince of darkness, taught me how to be a vampire and I was good at it. But then, a new darkness arose when I learned that my father was the supervillain that tried to steal mine and Ladybug's miraculous to wish for my mother back but failed so many times. He was not the father I know and he was sent to Hell where he can no longer harm the people I care most. I may be a bit of a killer but I have to feed or else I die. Marinette a.k.a Ladybug, is my love but I want her to remain human. I can't bear to turn her because I cannot take away her mortal life. That is if she wants to be one by choice I can but she should live her dream.
Adrien, now an adult, has a glass of blood at his mansion that was once his father's. He heard the mirror chiming and out came a man in gothic Victorian attire.
"Hello, father Dracula. I know it's been a year but I told you, I don't wanna turn anyone into vampires. I just feed on bad guy blood every night" Adrien said as he finished his glass.
"I see. Well, we just have to drain them to keep our youth and strength. So how's Ladybug doing right now?" Dracula said.
"She's doing great. Saving the day in the daytime. Living her dream as a fashion designer." Adrien answered.
"I see. Well, Paris has never been safer since we sent Gabriel to hell" Dracula said.
"Speaking of him, he's been visiting me from the fireplace. He can't step into the living world and I hope he doesn't try to get revenge on me. He brought it on himself years ago" Adrien said and offered a glass of blood to his new father.
"Yep. He failed to be a husband and father" Dracula said.
"Anyways, why are you here? Werewolves on the loose? Zombies trying to get to your castle? My cousin pulling a prank on you again?" Adrien asked.
"None happening but your cousin does like to pull pranks a bit. Harmless ones I'm used to. I came here to check on you and thought you would need my brides to assist in keeping your mansion safe" Dracula replied.
"I would like that, though milady is my only bride," Adrien said.
"I get it but mine will be there to protect the mansion," Dracula said.
"Very well. Just tell them to not get all over me. I like personal space, thank you" Adrien said.
"Sure" Dracula agreed.
x
Much later, Marinette came to visit the mansion. She loved her prince so much that he respects her to remain human.
"Oh kitty, where are you?" She called out and saw a bat flying from the stairs.
"Greetings Princess" He morphed into human form.
"Batty again to see me?" Marinette teased him.
"Yes, for my purretty lady" He kissed her hand.
He brought her upstairs to his bedroom and from there he waltzed with her, looking at his lack of reflection but her reflection was like she's dancing by herself.
"You may not be seen in the mirror but I can tell you still look good in pictures and videos," Marinette said.
"And you look so beautiful dancing without me in the mirror" He purred seductively.
"Oh, Adrien. Do you always have to be such a charming kitty?" Marinette asked and was dipped by him.
"Yes, for you," Adrien said.
"I'm always yours," Marinette said as he pulls her up.
"Something on your mind, my princess? Let me guess, Lila is trying to get to me, isn't she?" Adrien said and lifts her up like a ballerina pose.
"Nope, she's not" Marinette replied.
He then prickled his fangs on her neck, "I did warn her years ago. Now let's dance, my bride"
"Of course" Marinette held around his neck as they danced.
"And I know you're thinking about being immortal but I'm not ready to turn you" He twirled her, "You're the guardian"
"And you're the co-guardian. I haven't decided yet" Marinette said.
"It's up to you. What else could go wrong in Paris now?" Adrien said.
"I know you like danger but you know someone could use your blood to make money" Marinette stroked his hair.
"As if that's gonna happen. Not even Felix would allow that" Adrien said.
"You turned him, remember?" Marinette reminded him.
"I meant as in giving his vampire blood away," Adrien said.
"Oh right," Marinette replied.
"No one is gonna use me, milady. Vampires are very fast" He dipped her again.
"Faster than a speeding bullet, yes," Marinette said.
Adrien prickled her neck again with his fangs, "And very sexy too"
"Just because your teeth are dazzling and dangerous?" Marinette teased and moaned a little.
"Yep" Adrien replied and pulled her back up and kissed her lips.
Marinette kissed him back with passion. Adrien can hear her heartbeat and the blood rushing in her veins. After their dance, Adrien made the brides obey him to not attack Marinette just because she's human.
"Very well, she's your bride anyway," One bride said.
"And please, no attacking humans. If you do, I'll be sending you all back to your master" Adrien warned, not trusting them one bit. He did agree only for Dracula just to make him happy.
"Okay then," Another bride said.
"Sun is setting. You know what that means?" Adrien asked his lady.
"Protecting Paris from venomous vampires that you've been hunting for 3 years?" Marinette said.
"Yup. Lock your doors at home, my love. Be safe for me" Adrien kissed her cheek.
"Don't worry kitty" Marinette replied.
x
Once it was dark, Cat Noir went out patrolling on his own. Being a night guardian can be fun but hunting will one day get humans to discover his secret. He leaps up to Notre Dame to look over the city. Bats flying out of the Notre Dame tower, scattered in the sky like a swarm.
"My night exactly" He leaps off and turns into a bat.
He flew after the swarm of bats and felt the air breeze on him. After years of flying, he always loved the view of his home. Paris looked so beautiful from the skies as he flew. Right now, his mission is to find those evil vampires. He calls them venom vampires because their bite is like a snake and it can kill a human in less than a minute.
"Venom vampires here I come!" He dives down.
He knows they have no heartbeat and he can tell from one, "Where are you?" He morphed back to a human and took out his staff as an X-ray vision to detect heartbeats.
Everyone seems human with a heartbeat but there was one that was not. He smirked that he's got one and it was heading straight to the alley for blood and a bite of death.
"Time to drain him," Cat Noir said and follows him into the alley and saw what this vampire was trying to do; to drain an innocent stray dog. Cat Noir acted quickly and flashed in a speed of blur and stopped the vampire from scaring the dog.
"Animal cruelty is a very big punishment for you. Your teeth are filled with deadly poison" Cat Noir extends his fangs.
"Cat Noir! You always kill my kind! I'm not gonna end up like them!" The vampire backed away.
"Oh, I killed over 200 venomous vampires for 3 years" Cat Noir glared.
"This time I'll kill you!" The vampire growled.
"Not today," Cat Noir said but the vampire morphed into a devil bat to fly away.
Cat Noir chased him as a regular bat. As they flew to the roof, Bat Noir tackled the bat and both of them morphed back to human forms.
"You think you can get away with this, Cat Noir?!" The vampire yelled.
"I can" Cat Noir held out a holy cross and made it touch the vampire.
Cat Noir no longer fears because he got through it by praying to God that he's no monster to Satan.
"AAAAGH! IMPOSSIBLE!" The vampire screamed.
"This is the power of God!" Cat Noir said while tormenting the vampire.
"Stop it!" The vampire begged for mercy.
"Bon appetit!" Cat Noir sunk his fangs into the vampire's neck.
The vampire screamed in pain as Cat Noir sucked his blood.
Unlike regular vampires that die and turn to ashes, venomous vampires melt like acid.
"Dispose of evidence" Cat Noir stood up, watching the body melt into acid and just left the roof.
"Now time to get back to the mansion" He flew back home.