Chapter 7: My Cute Little Sister is the Strongest Hero
Author: Geraint
Nearly two years had passed, and my baby sister had grown so much. She was lying on my lap while I tickled her side, making her giggle.
"Gehehe~"
I sat on the couch, being silently judged by my parents and our maid. I was already sixteen and supposed to be attending high school—but I got into trouble on the first day.
It started when I bumped into a group of delinquent upperclassmen on the way to school. I was walking with Yuuka, Lilith, and Shiina at the time. They told me not to cause any trouble, especially on our first day.
But then those bastards tried hitting on the girls, their eyes practically undressing them. They ignored me when I tried to apologize for bumping into them. Then one of them touched Shiina, who looked scared and uncomfortable.
I snapped.
I gave him an iron claw to the face. A full-on brawl broke out. I broke my promise to Yuuka and Shiina. Again.
I sent all of those bastards to the hospital, and word spread quickly at school. I was immediately suspended for starting a fight.
Mom and Dad had a massive headache, forced to report to school on the very first day. Luckily, thanks to their influence, I wasn't expelled outright.
"For me, that suspension was kind of a blessing," I said, patting Fuyumi's head. "Now she won't be lonely at home."
"Gehehe~" Fuyumi giggled as I poked her nose.
"You should be glad it's only two weeks, Seir," Dad sighed.
"Who cares? I'd regret it more if Yuuka or Shiina got hurt. Even if I got expelled, I'd just go back to homeschooling."
"Well, those three girls came from an all-girls school and chose to transfer to a co-ed one just for you. They must be pretty disappointed."
"It's fine. We all live in the same house anyway," I said, lifting Fuyumi up and making her laugh.
I threw her gently into the air and cast a spell.
"Air Magic: Levitation!"
Fuyumi floated near the ceiling. I guided her flight with my finger, and she zipped around the living room joyfully. After a few loops, she came back, and I caught her safely in my arms.
"As expected, I can't get used to this," said Himiko-san, holding her head. "I'm going to lie down a bit." She quietly left the room.
When the girls came back from school, Yuuka looked irritated. As soon as she saw me, her expression hardened.
"Hmph," she said, turning away and stomping upstairs.
Shiina walked over with a guilty expression.
"I'm sorry, Yuki-kun... Because of me, you got—"
"Don't worry about it," I interrupted.
Her shoulders drooped, looking even more upset.
"I'm always giving people trouble. Yuuka and Lilith are always covering for me, and I just let it happen. I never even try to defend myself... I'm always the one being protected."
Tears welled up in her eyes. She was crying again.
"Here you go again—blaming yourself. It's not your fault for being pretty and having such a curvy body."
"Eh?!"
Shiina turned bright red, wrapping her arms around herself. She was very self-conscious about her body—especially her chest. She thought she looked chubby, but she really didn't. Her curves were just part of growing into adulthood.
"Go change clothes first. I want you to hold Fuyumi while I cook dinner."
"Okay," she mumbled and scurried upstairs.
"Lilith," I called.
She appeared, kneeling in her maid uniform.
"Yes, Seir-sama."
"How was school?"
"Nothing major. We got bored listening to the principal's long, scripted speech. Oh, and we're in the same class as that girl—Nishimiya Riko. She still remembers me. We became friends quickly."
"She asked about you a lot when we talked. She was really excited when I told her we'd be attending the same school."
"She even hugged me," Lilith added, clearly uncomfortable.
"Haha, that's just how she is."
Later, I was in the kitchen cooking dinner. Shiina stood behind me, holding Fuyumi in her arms. Unfortunately, Fuyumi had latched onto her chest.
"Uuuuugh... Fuyumi-chan, please, spare me... I don't have any milk! Yuki-kun, help me!"
Shiina's blouse was soaked in saliva, revealing her white bra. Her face turned crimson as she covered her chest.
"Don't look!"
"Okay." I turned back to the stove and focused on the food.
After dinner, I sat on the couch again, half-asleep, while gently patting Fuyumi, who snoozed in my arms.
Himiko-san came over to take her.
"Thank you for your hard work, Yuki-sama," she whispered, smiling softly as not to wake Fuyumi. She carried her upstairs.
I yawned. Sleep was about to take me when—
"Seir-sama! Seir-sama!"
"Shhh! Lilith, keep your voice down. Fuyumi is sleeping."
"Ah! I'm sorry, Seir-sama. I have great news!" she said excitedly.
She pulled out a glowing crystal ball. It floated above her palm, flickering with magic.
"I finally made contact with the other side!" she said, tears of joy welling in her eyes.
A woman with short pink hair and glasses appeared inside the crystal. She was sitting at a desk, surrounded by papers.
"Hey, Naamah! Can you hear me?" Lilith called.
"Naamah? Wait—is that really her?" I blinked in surprise. I almost didn't recognize her.
"Naamah, I'm with Seir-sama now. Like I said, he's alive. We successfully escaped the Demon King's castle."
Naamah looked up. Her eyes widened in shock.
No way... it's real! Seir-sama, you're really alive!
"What happened to you, Naamah? You used to dress a lot more... um, succubus-y. Now you're all professional. And your hair's short! Don't tell me—you got married?"
Naamah looked away, her mood dropping.
Listen to this, Seir-sama! My fiancé suddenly broke off our engagement! He said he preferred younger girls and that I was past his strike zone! I'm still 18! Waaahh!
I was supposed to be disgusted—but demons were always honest about their desires.
"Just forget that creep and move on!"
Seir-sama, you've gotten taller... and more handsome... Please cheer up this lonely old hag!
"You're only two years older than me! Get a grip!"
"Seir-sama," Lilith said, "I already spoke with Naamah. She has a way to open a gate... to return us home."
I should've been happy. But instead, I felt... conflicted.
"We can finally go home! Yay! Seir-sama, it's time for you to become the next Demon King!" Lilith cheered.
I turned to the side—and froze.
Yuuka and Shiina stood in their pajamas, having overheard everything.
"Onii-sama?"
"Yuki-kun... are you really going back?"
Yuuka's eyes welled with tears before she turned and ran upstairs.
"Yuuka-chan!"
Shiina hesitated, glancing back at me with a pained expression before quietly following her.
------------
I stood outside Yuuka's room and gently knocked on the door.
"Hey, Yuuka. Can we talk? There's something I need to tell you."
Shiina opened the door for me. Inside, Yuuka was curled up in bed, hiding under her blanket, softly crying. Shiina was about to leave, but I stopped her by grabbing her hand.
"Huh?"
"Stay with us."
I pulled her with me as we approached Yuuka. I sat at the edge of the bed.
"I'll be honest... I've been here so long, it's hard to imagine going back."
Yuuka peeked at me from under the blanket, listening.
"I don't care about the Demon King's throne anymore. I want to become a doctor—just like Dad. Everything's changed because of you all. I've gained so many important things here... I can't picture being happy if I went back."
I pulled Shiina in, and the three of us lay down together. I wrapped my arms around them, their heads resting on my shoulders. I could feel their warmth as I held them close.
Yuuka said nothing, but she nestled her face into my chest. Shiina, meanwhile, blushed so hard she fainted in my arms.
Both of them fell asleep beside me, so I stayed and drifted off with them.
Morning came, sunlight streaming into the room as birds chirped outside.
"Hm?"
"Good morning, you three," Mom said, arms crossed and frowning.
Mom and Dad were both standing by the door. Himiko-san had just opened the window, which had woken me up.
"Oh, good morning, Mom, Dad, Himiko-san."
Yuuka and Shiina sat up, rubbing their eyes.
"Yuki-kun, I heard from Lilith," Mom said with a worried tone. "Are you really going back?"
"I've thought about it... but I've decided not to. I can't bring myself to leave everyone behind."
"I see... That's a relief."
But then Mom's expression twisted into a scowl.
"Yuuka! Ayaka! What are those outfits?! You look like kids! How are you supposed to seduce Yuki-kun and keep him from leaving like that?!"
"Eh?!"
The two girls froze in place as Mom scolded them. Dad stayed quiet while Himiko-san pretended not to hear.
"Yuuka! You're in high school—why are you still wearing panties with bear prints?!"
"Mooom! Onii-sama is right here!" Yuuka turned beet red.
"And you, Ayaka!" Mom pointed at Shiina's chest. "That bra's way too small for your F-cup! You need to buy a new one!"
"F-cup?" I glanced at Shiina's chest, surprised.
"Kyaaah! Stop looking, Yuki-kun!" Shiina quickly covered my eyes with her palm in a panic.
"Uuuu... uwaaah! Uwaaah!"
Fuyumi's cries echoed from her room. I jumped out of bed immediately.
"Fuyumi! Onii-chan's coming!" I bolted from the room at lightning speed, leaving everyone stunned.
Downstairs, I cradled her in my arms, gently patting her back after changing her diaper. She was still sleepy, so I let her rest on my shoulder.
In the living room, I spotted Lilith seated on the floor, speaking to Naamah through the glowing crystal orb on the table.
"Good morning, Lilith."
"Good morning, Seir-sama," Lilith yawned, bowing half-heartedly.
I sat on the couch behind her. Naamah, visible inside the crystal, gasped.
"Seir-sama... you have a child?!"
"She's my little sister. My adoptive parents' daughter."
"Oh, thank goodness," Naamah sighed with relief. Her face grew serious.
"Seir-sama, I have bad news."
"Hm?"
"Demon King Balan—your father—disappeared two years ago. No one knows where he is."
"Don't really care. Who took over? The First Prince?"
"Yes... Prince Eligor is now the top candidate."
Eligor, my eldest brother, wasn't exactly impressive. I'd fought him a few times—loud bark, weak bite. My stronger brothers had long since stopped bothering to challenge him.
"Strange..." I muttered.
"Seir-sama?"
"We all used to compete fiercely for the throne, but one by one, my brothers backed out. It's odd that only Eligor and I remained in the end."
"Umm... Seir-sama, have you heard about the divination?"
"Divination?"
I hadn't.
"There's a prophecy... that a hero will appear—one strong enough to destroy all of demonkind. Even the Demon King would be powerless against them. I'm afraid not even you could defeat this hero."
"Someone stronger than the 'puny' heroes I've crushed in the past?" I smirked. "Sounds fun."
"This hero is unlike any before. They possess seven divine relics."
Lilith's eyes widened in shock.
"Seven?! That's insane! Seir-sama has most of the twelve relics already, and no human should be able to wield more than one or two! Every past attempt to hold two relics has ended in death! How could someone manage seven?!"
She slammed her palm on the table in frustration.
"But the prophecy came from the old demon sage," Naamah said. "And his divinations have never been wrong. This hero will appear soon. All of demonkind is in danger."
"Don't worry," Lilith said. "Seir-sama and I will protect the relics. Besides, we're in another world right now."
Even so, Naamah still looked troubled.
"I have a description of the hero," she continued. "They are a young human with long dark purple hair and glowing purple eyes. Their divine relics form radiant marks across their body. Their presence alone can destroy low-level demons. Be careful, both of you."
Something about that description... felt familiar. But it couldn't be. The age didn't match.
"Don't worry," I said confidently. "I've hidden the divine relics. No one's going to find them."
"As expected of Seir-sama! Where did you hide them?" Lilith asked eagerly.
"Heh... Most of them are sealed inside Fuyumi."
"...What?" Lilith and Naamah froze.
"Something wrong?"
Lilith pointed at the little girl in my arms.
"Dark purple hair... and purple eyes... Seir, don't tell me—how many relics did you seal inside her?"
"I think... about seven?"
My face turned pale as I looked down at Fuyumi.
"Gehehe~" she giggled innocently, snuggling closer to me. Her cuteness made my worries melt.
"As expected from Fuyumi. This demon prince has no choice but to surrender to such a cute little hero." I tickled her gently, and she laughed.
"SEIR-SAMA!!!"
"Seir-sama! What have you done?!"
I burst out laughing while Lilith shook me furiously.
"Hahahaha!"
"You just created what you were supposed to destroy! Now the entire demon race is in danger because of you!"
"Shut up! I didn't seal those divine relics inside Fuyumi to fight demons—it was to protect her!"
"In the first place, how did you even seal them in her body without harming her? Possessing two relics alone is enough to kill a person!"
"I know that. But I didn't think just one relic was enough to protect her. So I thought long and hard about how I could let her possess more without risking her life... and I came up with an idea."
"What?! There was a way?!" Lilith was in shock—so was Naamah, who had been watching us through the crystal ball on the table.
"I'll do anything to keep Fuyumi safe. That's why I reforged the divine relics—by fusing all seven into one weapon."
"No way! Those relics are indestructible! They were made by the gods!" Lilith trembled.
"Yeah, it took me months and it was incredibly difficult, but I did it. The result was a katana—one I sealed inside Fuyumi's body. Someday, when I'm not around, the blessings from all seven relics will protect her from any harm."
Lilith dropped to her knees from what she just heard. Yuuka and Shiina, already in their school uniforms, came up behind her and grabbed her arms.
"Lilith, what are you still doing? We're going to be late! Hurry and change into your uniform!" Yuuka scolded her.
"Wait! I still have something important to tell Seir-sama!"
"You can do that after school! Do you want to get punished by the homeroom teacher?"
"Wait! Waaah! Seir-sama, you dummy!" Lilith cried helplessly as I just waved at them with a smile.
"Seir-sama," Naamah called out from the crystal ball, her voice serious.
"I just want to confirm something... Did you feel anything strange around two years ago, when the Demon King disappeared?"
"Hmm... I haven't fought anyone seriously since we arrived in this world. I feel the same as always. Maybe I'm getting rusty."
"I found something in the records left by past Demon Kings. It's about the 'Throne.' It says the real Demon King doesn't ascend to the throne—the throne chooses its king."
"...What?"
"Wherever the real Demon King goes, the Throne follows. In other words, Seir-sama... the Throne is with you. I believe the previous Demon King vanished because the Throne abandoned him after you defeated him."
"You mean..."
"Yes. He's no longer recognized by the Throne. It's already transferred to you. Seir-sama, whether you realize it or not, you've already been chosen as the true Demon King."
"And how are you so sure?" I frowned.
"You told me you reforged the divine relics, right? That means you had to destroy them first. Only a true Demon King can destroy those relics—they were meant to be indestructible. Out of the original 21 divine relics, 9 were destroyed by past Demon Kings."
Naamah stood and knelt before me, bowing her head low.
"Hail to our true Demon King. I, Naamah, one of the Seven Disaster Witches, pledge my loyalty to you."
I sighed. Just like Lilith, now Naamah was treating me like a Demon King too.
"Okay, then. As your new Demon King... no matter what happens—everyone must remember this: Fuyumi will always be the cutest little sister in the world!"
"Yes, Seir-sama!"
After a brief silence, Naamah blinked twice and gave me a puzzled look.
"...Huh?"
"Exactly. That's the most important thing. Never forget that, understand?"
If what she said is true—that the Throne is in my possession—then the surge of demonic power I felt two years ago, when I swore to protect Fuyumi, was the moment I became the true Demon King. I always thought it was my love for my little sister that made me stronger.
"Yes, Seir-sama..." Naamah responded, still a bit weirded out.
Since we were speaking in a demonic language, none of my parents or step-siblings understood the conversation—but I could tell they understood one thing: Fuyumi. Their curious stares confirmed it.
"Anyway, what's the current situation over there?"
Naamah leaned back into her chair, exhausted.
"Many demons aren't happy with the new Demon King. The nation has split into factions, each supporting their own candidate."
She slammed her fist on the table in frustration—then winced in pain.
"Ouch! Ow, ow, ow!"
"What are you doing?"
"His rules are absurd, and he abuses his authority constantly. He even sent letters to the heads of every demon clan, demanding they send their most beautiful daughters to become his wives. I received one, too, but I refused. I'd rather be a fugitive than marry that creep!"
"I don't see the problem. He's a Demon King. It's his duty to have many concubines to ensure strong heirs. Otherwise, the next generation might be too weak to survive the wars with humanity."
"I don't care! That guy isn't worthy of being Demon King! Our nation is falling apart under him! The only Demon King I will ever serve is you, Seir-sama!"
"You and Lilith praise me too much."
"That's how respected you are, Seir-sama. Even if you're a fugitive, many demons admire you. You're kind to allies and ruthless to enemies. You have all the traits of a true Demon King. You even defeated the last king in fair combat. With the Throne in your possession, you are the rightful ruler of our nation."
She bowed once again.
"Please, Seir-sama. Return to us. The Demon Realm needs you."
I looked at her, then down at Fuyumi in my arms.
Both worlds needed me—but I had already made my choice. The Demon Realm would be fine without me. But Fuyumi... she needed me more.
"Sorry, Naamah."
She closed her eyes sadly. "I see... just like Lilith said."
"Yeah. I'm not interested in being Demon King anymore. I've got more important things to take care of here."
"Then... how about this?" Naamah asked with determination.
"If I find a way to travel back and forth between worlds—will you accept the throne?"
Those words lit a spark in me. That way, I wouldn't have to abandon anyone.
"Definitely," I grinned.
"Then I'll make it happen. For the sake of the Demon Realm, I'll find a way."
She put a hand over her heart and saluted.
I glanced at Fuyumi in my arms. She mimicked my grin and giggled softly.
"Guhehe~"
(To be continued.)