(In Rosario Vampire, Moka's Rosario was placed on her sometime after her 11th birthday and then she was sent into the human world. I will say Tokyo since why not? She went to Junior High in the Human World for three years then High School at Yokai Academy.
I am also making the events of Vampire Rosario take place before the DxD and Shinmai. Jack and Moka were both born in 1988, Jack on September 20th, and Moka on May 8th. Meaning when Moka and Jack finish high school, the year will be 2006, two years before the DxD and Shinmai events happen. Three years after Slash Dogs events, taking place in 2003.)
Two weeks after the talk with his parents and learning under them, he took a rest day. While he liked improving more than anything, he did see the benefit of proper rest. As such, he decided to explore more of Tokyo as it was a big city and he hadn't even seen all of it.
Early in the morning, he left his house with Amara as always taking her spot on his shoulder. It was a good thing he was so big and muscular as Amara was getting big and heavy. She weighed 20 pounds and quite large as her breed should be.
He walked past Aya's house knowing that girl she would be sleeping until noon on a nonschool day. He hadn't even been to school in two weeks and he expected his teachers would get in contact with his parents soon.
Regardless, the school had lost its purpose in his life as unlike Rias Gremory who went to school because she found it fun, he didn't. He knew that thanks to Other Jack who moved to Kuoh with his parents when he 16.
When he transferred to Kuoh, his Supernatural disposition was discovered early, but he refused to join any Peerage. By the time Issei joined the peerage of Rias Gremory, Other Jack was dating Akeno.
He and Rias were friends, but not dating because they simply didn't get along. Other Jack found Rias' constant attempts to turn him into a Devil creepy and disrespectful. She disliked his constant rejection as this had been before the Rating Game with Riser.
"Apophis, you who spent a year with the other Jack, what did you think of him? Truly."
[What did I think of him? I respected him since he was a normal human who reached the highest point. Even before I was sealed into his Twice Critical, he had already been considered one of the most powerful humans.
He had evolved his Twice Critical by absorbing a gem of The Boosted Gear following a fight with Issei Hyoudou. He had achieved not just a Sub Species Balance Breaker, but an Abyss Side Balance Breaker in his battle against Kokabiel. The Dominator's Stand."
Jack nodded as he remembered that memory vividly in Other Jack's mind. The Balance Breaker had a few forms, Crest Side which was the normal Balance Breaker. Sub Species, a personalized Balance Breaker made from the user's desire.
Then the Abyss Side which was the fusion of the Crest and Sub Species Balance Breakers and improved by the user's desire for more power. Achieving that not only gave Other Jack enough power to survive the battle against Kokabiel, but he even managed to claim the Fallen Angel's right arm.
His power had then soared to new heights when his mastered Twice Critical was implanted with Apophis sealed in a gem of the Diabolos Dragon God. He had then been blessed by Ophis as she had done for Vali and Issei.
He had then died in the battle against Ragalzeva when he reached Earth with his Devastator Order to allow his lovers to escape. Then, his splintered soul had fused with him starting him on this path.
"Such his fate I g-"
"LOOK OUT!"
Just as he was talking, his instincts fired awake making him jump back to avoid a bike hitting him on the head. His eyes shot for the person on it and he saw a pink-haired girl around his age.
She was kind of short, and she was wearing a odd silver Rosary around her neck. Rather than focus on her, he focused on her speed as she was moving faster than any human had any right to on a bike.
'Fast.'
He moved quickly and he grabbed her by the back of her shirt and her bike at the same time. Amara jumped away as he spun around to stop the girl's momentum before coming to a complete stop.
"Wow there, you ok?"
When he did come to a stop, she sighed in relief she didn't hit him.
"Sorry about that, Sir. I will be more careful."
He put her down and her bike at the same time which was in one piece.
"You are fine, but I am not a sir. I am ten years old."
The girl seemed taken aback so she rubbed her eyes a few times before looking back up at him.
"Are you sure?"
He nodded as despite his size he wasn't even 11 yet. Since today was August 22nd, his birthday wasn't for another 29 days. He didn't focus on that as this girl didn't seem mundane. First of all, her bright pink hair stood out like his blue hair and Aya's red.
Second of all, her unique Rosary was giving off a lot of aura. It was far more than should be normal for a magic necklace, but the girl herself had quite a bit of Mana, just not all that much.
"I am. My name is Jack Owens, I go to Hijigazaka Middle School. It is my last year before I go to Junior High."
She suddenly clasped his hands ignoring his massive size.
"REALLY! I am transferring there on Monday. What is it like? I have never been to a human school. I am Moka Akashiya, I'm a Vampire."
When she said that, an old lady who was walking by shook her head.
"Kids and their imaginations. Young man, I recommend you make your daughter stop playing pretend."
Moka seemed surprised as the old lady continued on her way. Jack didn't say anything as he picked Amara off the ground.
"Moka, have you never heard of the Statue of secrecy?"
She shook her head.
"No, what is that?"
He waved his hand and released a wave of mind-altering magic causing all the humans to stop paying attention.
"We Supernatural entities are supposed to keep our existence secret from the humans. You can't just go around telling people you are a Vampire. That is just asking for the Hero Clan to come kill you."
She gasped as if she had forgotten about that.
"I'm sorry."
He shook his head as he began to continue his walk.
"I do have to say you don't seem very Vampire-like. Are you sure you are a Vampire?"
"I really am."
She opened her mouth showing her sharp fangs.
"See."
When he saw that, he nodded.
"Do you drink blood, sleep in a coffin, and turn into a bat?"
"I do drink blood, I don't sleep in a coffin and I can't turn into a Vampire. You see, I used to be much scarier, but then I had this Rosario placed on me."
She held the Silver Cross and showed it to him.
"I was told that if I ever removed this, I would turn into my true form, a powerful frighting Vampire. How about you?"
Since his magic was keeping everyone controlled and technology couldn't film him in this state he showed her. From his back, his two sets of draconic feathered wings.
"I am a Dragon Fallen Angel hybrid. You do know what Fallen Angels are right?"
She frowned before nodding.
"Yes, my Dad sometimes makes deals with one of them. Boring business talk and stuff. He is tall, has blonde and black hair, and likes to talk. Really strong too."
He retracted his wings before he pulled his phone out and showed her a picture of Azazel.
"Is it this guy?"
When she looked at her phone she nodded almost surprised.
"YES! That is him. The Angel General or something."
"God damn it."
He instantly began to go to his contacts before he called Azazel himself. It only took a few moments for the Governor General to respond.
"Jack, how are y-"
"No time, tell me if you know a Vampire girl by the name of Moka Akashiya."
Azazel nodded.
"Not directly, I know her Father Issa Shuzen, head of the Shuzen Vampire Family of Japan. One of the strongest Vampires in the world. Everyone knows of the Romanian Vampires of the Carmilla and Tepes lines, but most humans don't know about the Japanese Vampires.
The Japanese Hero Clan tried to wipe them out, but they failed spectacularly because of Issa and his family. Both Vampire lines were started by Dracula in Ancient Times but branched off in the 15th Century when his kingdom the first Vampire Monster Kingdom was destroyed by humans. Dracula who changed his name to Alucard then went East.
The Vampires left behind and then started the Tepes and Carmilla Lines away from his influence. Only that Dracula was beyond unique, he was a Shinso Vampire. Consider them, Super Vampires. Very strong, Immortal, and dangerous as shit.
Dracula was a calamity as when his kingdom was destroyed he began absorbing other Monsters, and Supernatural entities for power. Turned into a nearly immortal monster that many Pantheons were going to put down. Much like Ddraig and Albion several Factions were going to put an end to him, but we didn't have to do much.
He was sealed away by three very powerful Monsters or Yokai as they call themselves The Three Dark Lords. Edgy as hell, I know, but they are the real deal. Akasha Bloodriver, Tenmei Mikogami, and Touhou Fuhai. Some of the strongest Yokai in the world. Since I didn't have to do anything, I felt the situation solved itself. Now, how did you meet Moka?"
Jack looked down at Moka who was listening in.
"She said she got sent out to live in the human world. She almost hit me with a bike and she was openly telling me about her being a Vampire."
"That's not good. Tell her not to do that. I will give her dad a call. Later."
When Azazel hung up, Jack put his phone in his pocket.
"You heard him, from now on don't tell humans what you are. It will end badly since you are sealed right now. Now, are you living alone?"
Moka nodded.
"Yes, when I came to the human world, Sir Tenmei Mikogami placed me in a paid-for house. My Father said independence would do me good."
"You are telling me, an 11-year-old girl got sent to live by herself. Vampire or not with no knowledge of the human world by herself?"
Moka nodded with a sheepish smile.
"Yes."
He sighed as he knew if she kept going around telling people she was a Vampire it would bring her danger. If something happened to her, her family and the Dark Lord Guy would certainly be pissed.
"As a fellow Supernatural Entitity, I might as well show you the ropes of living in the human world. I know we just met, but want to come to my house. My mom is a Witch."
"OK! Will you be my friend?"
"Sure, I don't have many friends."
"Me neither, now we have one more each."
She seemed so sweet, it made him smile. He began to lead her in the direction of his house, but just as they were passing Aya's house she saw him out the window. She pressed her face against the glass as she saw her best friend with another girl.
After ignoring her for two weeks here he was hanging out with someone else. She ran out of her room, down the stairs and she pushed the front door open. Jack who had been walking turned his head as Aya came out sprinting full speed.
[Lady trouble?]
'Seems like it.'
"JACK!"
Moka made a sound reminiscent of a bat and hid behind him as Aya reached him.
"What?"
She took a deep breath before looking at him with squinted eyes.
"What gives?"
He knew what she was talking about.
"Sorry about missing out on the last two weeks of school and our usual meet-ups. I was busy."
Aya with squinted eyes turned to look at Moka.
"Busy? With what?"
He smirked as he looked at his best friend. Only friend really and like Apophis put it, someone he cared about. He might as well come out with it since he didn't see a reason to keep this hidden any longer.
"I was learning magic from my Mom and fighting skills from my Dad."
Moka craned her head up at him as he just said they weren't supposed to talk about it. When Aya heard it she tilted her head in confusion.
"Magic? Magic is real?"
He nodded.
"Yeah, my Mom is a Witch."
Aya just scowled as it seemed he was insulting her favorite neighbor.
"Hey, leave miss Esmeralda out of this. No way a nice lady like her is a Witch."
Jack rolled his eyes as he held his hand in front of Aya. He opened his hand causing a small black fireball to float above his palm. When she saw the fireball, she looked at it before shaking in excitement.
"COOL! Your mom is a witch?"
"She sure is. Want to learn magic from her?"
Aya bobbed her head up and down much like he had when his mom asked if he wanted to learn. First, he placed his hand on her head before giving her a quick scan as Azazel had taught him.
It was to check if someone had talent or had a Sacred Gear. When he did so, he found that unexpectedly, his friend did have a Sacred Gear. Just having that would make her future far easier.
'Which one is it though?'
(In Shinmai, Vampires are nearly extinct since the Hero Clan killed most of them. Not possible with the strength of DxD/ Rosario Vampires. One of them, Nanao Tachibana is a half Vampire and in Shinmai Dhampirs are weird. They change genders between male and female until they are 18 years old and then they stick to the one they like. Basara caused her to turn female permanently getting her pregnant.)