The Lucifer's Greatest Treasure

Prologue

Four year old Issei Hyoudou waited for his mother to come. He was ecstatic to meet his new sister. His parents couldn't have another one, so they decided to adopt a girl. The door opened, and a blonde haired girl was holding on to a rabbit stuffed animal. She held Mrs. Hyoudou's hand and hid behind her when she saw Issei. "Issei, this is your new sister, Serenity Hyoudou. Serenity, this is your new brother Issei." She looked at Issei, and her new mother nudged her out from behind her legs. Serenity hid behind the rabbit that was as nearly as big as her. Serenity was extremely malnourished. Mrs. Hyoudou knew that it would take time for Serenity to become healthy again, and she was patient enough to help the girl. Issei ran towards Serenity, who screamed and tried to run away, as she got hugged. "I'm going to protect you now." Issei said. "I'm your big brother." Serenity slowly hugged him back. Mrs Hyoudou smiled and took a picture.

"Serenity dear, do you want cake?" The girl nodded frantically, excited for cake. She's never had it before, and she pulled Issei with her towards the kitchen. They sat at a little table and waited for cake. Serenity got a slightly bigger piece than Issei. "Now Issei, Serenity needs to eat lots of food so she can gain weight." The young boy nodded and tried to feed Serenity his cake as well. Serenity shook her head and ate her cake slowly. Mrs. Hyoudou grabbed the camera and took a picture. Serenity had chocolate icing around her mouth, and Mrs. Hyoudou laughed.

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Issei felt his sister crawl into his bed. The now ten year old siblings were inseparable, and Serenity snuck into her brother's bed to keep the nightmares away. He felt her snuggle into his warmth, and they both fell asleep. Mrs. Hyoudou came to check on them and smiled. She was glad that Serenity was healthier now. She was still small, but her biological mother was small as a child. Mrs. Hyoudou frowned, and what her daughter witnessed when she was three was something no child should witness. She had to wait to adopt Serenity after she was found running around. The girl was covered in blood, and the police figured out that Serenity watched her biological parents get killed. Mrs. Hyoudou went to bed.

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"Issei-nii!" Serenity yelled. The boy ran downstairs and saw his sister in the girls' Kuoh Academy uniform. She had on her cloak and smiled at her brother. "Don't be a pervert." Serenity stuck her tongue out. Issei grabbed her hand, and their mother took pictures. Serenity's brown hair was in a french braid, and Issei frowned. "What's wrong?" Serenity asked.

"The boys are going to flirt with you." The boy frowned. Serenity shrugged her shoulders.

"I'll have you to protect me." Serenity said.

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"I'm Serenity Hyoudou. Please take care of me." Serenity bowed down. The girls cooed at Serenity.

"And I'm Issei Hyoudou. I like admiring female bodies." Serenity face-palmed and hit her brother in the head.

"Excuse my brother, he's a bit of a pervert. But that's just his hormones."

"If any of you boys touch my sister, I will kill you dead." Serenity shook her head, and they sat down.

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"I got a girlfriend!" Issei said. Serenity frowned and shrugged her shoulders. "

"I bet she was desperate." Serenity teased. Her hair was down to her shoulders, and they were both seventeen. Serenity hugged her brother and smiled. "Though I'm happy for you. Maybe you can get laid." Serenity said. Issei blushed.

"I need help." Issei said. Serenity helped Issei with his plan to take his girlfriend on a date.

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"Nii-san, get up!" Serenity slammed open the door and saw Issei and a crimson haired beauty in bed together. "Mom! Issei has a girl over, and they're naked!" Serenity slammed the door shut, and Issei sighed.

"That's your sister?"

"Adopted sister." They got dressed, and Rias explained why she was in bed with Issei.

"Wow, Issei, you have a beautiful girl in bed, and you still can't get laid!" Serenity said. Rias blushed and shook her head. "Is this your girlfriend?" Rias's eyes widened. She thought she erased her memory of Issei's girlfriend. She was curious about what the girl was.

"No, we're not dating." Rias said.

"Oh, ok. I figured what I walked into was that you two were together." Rias mentally sighed in relief. "I got to go, Issei-nii." She kissed her brother's cheek and ran outside.

"Your sister is adorable." Rias said.

"Oh yes, Serenity and Issei are pretty much inseparable. I have a feeling that Serenity will lose her virginity before Issei, though." Rias jumped as Issei slammed his hands on the table.

"The boy better marry her first."

"Or girl." Mrs. Hyoudou said. "Your sister likes both genders."

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"This is Asia Argento." Serenity smiled at the blonde haired girl. "She can also learn to be a good wife." Serenity choked on her drink, and Issei rushed over to help his sister.

"I'm fine."

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"Ah, Rias." Serenity said. "Thanks for keeping my room the same." The red-headed girl nodded, and Serenity went outside to go get the Ayato Kirishima blanket that her mother had gotten her. Serenity skipped her way towards the shop and saw her chemistry teacher. "Ah, Azazel-sensei." Serenity said. The man turned around.

"Hello, Ms. Hyoudou. What are you doing out here?" Serenity smiled and showed him the blanket. Azazel laughed and decided to walk the girl back.

"Mr. Azazel, what's a fallen angel?" Serenity asked. Azazel decided to take Serenity out to eat and explained the supernatural world to her. "Thank you for telling me the truth. Since Rias showed up, Issei had been ignoring me ever since. How about we keep it a secret between you and me?" Serenity said. The Fallen Angel frowned and nodded.

"And when you feel lonely, you can come play games with me." Azazel ruffled Serenity's hair and walked Serenity to her house.