Chapter 3: The Mob Prince Protects His Sister from a Demon
──And then, in the blink of an eye, four years passed, and I turned five.
During these four years, I never stopped using [Dark Edge] for even a moment.
“Look, Diana, scary~, it’s the Demon Lord!”
“Aha, Onii-shama, shugoii!”
I was playing Demon Lord with my four-year-old sister, Diana.
I generated two [Dark Edge] blades from my forehead like horns, puffing out my chest proudly like a villain.
That’s because the Demon Lords in the stories Mom reads to us have horns.
Now, I could produce [Dark Edge] from places other than my palms.
This way, I could keep using [Dark Edge] while playing with Diana.
Diana clapped her hands and rejoiced.
Alright, I did it, she liked it.
Luna-sama was suddenly summoned by the Emperor early in the morning and hadn’t shown her face.
If that’s the case, I have to take good care of Diana.
“The Demon Lord kidnaps princesses. I’m going to catch Diana!”
“Kyaa, Diana, running away~!”
And so, we started a game of tag in a room too big for children.
As always, no one other than Mom rarely ever comes to this Prison Tower.
The current environment, with little contact with others, can hardly be said to be good for raising children.
That’s why I made sure to play with Diana every day until she was satisfied, so she wouldn’t feel lonely.
Fortunately, there are plenty of picture books and toys here.
“Caught you! From today on, Diana is mine, the Demon Lord’s!”
“Uhya! Happy, Diana. Becoming Onii-shama’s. Marrying Onii-shama!”
When I hugged her, the precocious Diana blushed and returned the embrace.
Diana declared that she wanted to marry me in the future.
W-What is this cute creature?
My little sister is too cute…!
I can’t believe that Diana, who is like this, will become a Demon Lord who brings terror and destruction to the world in the future.
After all, it’s because the upbringing environment was too poor.
If I protect her properly and shower her with love, the future where Diana falls to the dark side and becomes a Demon Lord will never come.
“Okay, now it’s Diana’s turn to be the Demon Lord.”
“Yeah, Diana, catching Onii-shama! Kneel before the Demon Lord Dianaaa!”
Diana became the Demon Lord and chased after me.
Diana had somehow memorized the Demon Lord-like lines.
She’s still only four years old, but amazing. My little sister is a genius.
“Whoa, that’s pretty good! But Diana, you can’t become a Demon Lord in the future, okay? If Diana becomes a bad Demon Lord, I won’t marry you.”
“Eeeh!? I don’t want that!”
Diana puffed out her cheeks and stomped her little feet.
“Then, I’ll stop being a Demon Lord!”
Whoa. She’s saying something I’m happy to hear.
“No, no, that’s a story for when you grow up. I want Diana to chase me now!”
“Yay! I did it!”
I savored the unchanging happiness of my daily life with Diana.
But, the next moment…
It happened suddenly.
A raging heat overflowed from the depths of my body.
“Atsuuu!?”
I couldn’t help but squat down on the spot.
This is a Magical Runaway after a long time. I had been feeling that my Magical Power was increasing recently, but… this one is quite intense.
“Onii-shama!?”
“Diana, stay away, it’s dangerous!”
I stopped Diana, who had rushed over to me, with my hand.
“[Dark Edge]!”
And then, I generated a huge [Dark Edge] from both hands that reached the ceiling. This is the result of four years of training.
It wasn’t in the game, but when I accumulated a lot of [Proficiency], I became able to freely change the size and shape of the [Dark Edge].
The larger the giant [Dark Edge], the greater the Magical Power consumption. I thought this would quickly stop the Magical Runaway, but…
“Are you kidding me!?”
Magical Power that seemed infinite was gushing out at a rate that exceeded the consumption.
W-What is this…? Could it be that I am destined to die after all?
“Okaa-sama! Onii-shama is in trouble!”
Diana shouted towards the door of the room, but there was no response. Mom hasn’t come back yet.
Then, I have no choice but to do something myself.
“Make an even bigger [Dark Edge] and use up all my Magical Power…!”
I made the [Dark Edge] even bigger and made its tip reach the ceiling.
Then, there was a booming sound, Zubaāān!
“What!?”
A large magic circle floated on the ceiling and repelled the [Dark Edge].
Due to the impact, my [Dark Edge] disappeared.
…T-That’s right, I messed up.
This was a Prison Tower to keep Mom locked up.
When you try to destroy the Prison Tower with magic, a barrier magic is activated to prevent it.
“Detecting an attempt to destroy the Prison Tower. Subjugating the caster.”
An inorganic voice echoed, and the space near the ceiling distorted. It’s the Summoning Magic effect that I’ve seen many times in the game.
With a roar, a huge demon-type monster with jet-black wings appeared from there.
“Guoooooooon!”
“Kyaaaaaaa!?”
Diana’s legs gave out.
Is this a [Summon Trap]? It’s a magic trap that summons monsters to intercept intruders into treasure vaults and the like.
Moreover, what was summoned was an A-rank equivalent monster──an Archdemon, a high-ranking demon.
My knees trembled involuntarily.
To have such preparations…
Emperor Alvaise has no intention of letting Mom escape from here.
“Could it be that you are the impudent one who is trying to destroy this Prison Tower and take away the Dark Elf princess?”
The Archdemon stared at me with embers-like red eyes. Unable to withstand the weight of the landed giant, cracks ran across the floor.
“Such a child? Well, whatever. The contract was that I could devour any impudent person! A young child is truly the finest offering.”
The Archdemon licked its lips and looked down at us.
This guy, could it be…
“Wait. If you try to lay a hand on my sister, I won’t forgive you!”
I generated [Dark Edge] again and readied myself.
My heart shrinks with fear, but this guy was summoned because of me. Then, I’ll protect only Diana, even if it costs me my life.
“O, Onii-shama!?”
“Diana, hide behind me!”
I shielded my sister and stepped forward.
“[Dark Edge]? Are you trying to resist with such low-level Dark Magic?”
When the Archdemon held out its hand, countless fireballs were created and rushed towards us.
“I’ll burn you to a crisp.”
“Mine isn’t just a [Dark Edge]!”
I enlarged the [Dark Edge] and covered myself and Diana.
The fireballs exploded against the [Dark Edge], creating holes, but I used my Magical Power to quickly repair them.
“No matter how much you attack, it’s useless! I have Magical Power to spare!”
It’s a terrible attack, but I’m somehow managing to withstand it.
If this Archdemon is part of the intruder interception system to prevent Mom from escaping, then soldiers who have received the news should be rushing here.
If I can buy time like this, I can protect Diana even if I can’t beat this guy.
“What…? Interesting! Then, I’ll gradually increase my Magical Power. How long can you endure?”
The Archdemon showered me with even more fireballs.
Moreover, the power is increasing more and more.
Is this guy playing with me?
Damn it. At this rate, I’ll be overwhelmed.
“Onii-shama!?”
Diana raises a worried voice.
But, I promised Mom that I would protect Diana.
If a Magical Runaway is happening, it’s actually convenient. I’ll squeeze out all the Magical Power in my body and try to counter this guy.
Bigger, harder, thicker, a [Dark Edge] that goes beyond the realm of swords…!
“Alright, this is the end!”
The Archdemon created an exceptionally large Fireball and slammed it down.
Dogoooooooon!
An explosion occurred that shook the entire Prison Tower.
But neither the flames nor the impact reached us siblings.
“Impossible…? W-What is that?”
I transformed [Dark Edge] into a thick, large shield. It became a shield as sturdy as a castle wall.
“I call it [Dark Edge Wall]!”
“My ultimate magic is not effective!?”
The Archdemon trembled in astonishment.