I Became the Younger Brother of the Villainess

If my sister hadn’t wasted time trolling in the main story—if she had trained instead of chasing after the prince—she could have been stronger than any of the named characters in the original plot.

Tsk.

And that 「Devotion」 trait? It might seem positive at first glance, but knowing what happens when my sister meets the prince, I can’t help but feel a chill run down my spine.

Why would someone as kind, beautiful, and adorable as my sister turn out the way she did in the main story? It had to be because of that trait. At that level, it wasn’t devotion—it was obsession, bordering on madness.

Clicking my tongue, I continued my training.

Regardless, I had my overpowered unique traits, so even with my lack of real combat experience, I figured I wouldn’t get completely destroyed.

But more than that, I wanted to look cool in front of my sister.

The day of our sparring session arrived, exactly a week after I first brought it up.

I’d considered waiting longer, training more before facing her, but I doubted it would make much difference. I’d already done everything I could on my own. The next step was real combat. And frankly, going outside the estate to fight for experience felt like a hassle.

Fighting common bandits or highwaymen wouldn’t offer me any real challenge or insight, and finding a proper opponent elsewhere seemed unnecessary when the best one lived under the same roof.

Besides, I was confident.

Confident enough not to embarrass myself too much, at least.

“Are you ready?”

“What about you, Sister?”

“I’m always ready.”

“Good. So am I.”

My sister smiled at my response—a sharp, confident grin. She wasn’t wearing her usual gothic-style dress today but a sleek, black bodysuit.

Honestly, it was so tight and revealing that it nearly threw me off. If we weren’t in the basement, I might have thought she was teasing me on purpose and tried something inappropriate.

In contrast, I was dressed in a simple robe befitting a mage. Not too long, not too short. I didn’t even have a staff—could I really call myself a mage?

“What are you staring at?”

“Just curious. Do people usually wear that for sparring?”

Noticing my gaze, my sister asked, and I responded with an honest observation and question.

“Oh… uh, well… it’s unavoidable. I use blood to create my weapons and armor, so…”

Blushing slightly, she hurriedly explained. The gist of it was this:

Every time she fought, her blood would envelop her body to form weapons and armor. Whatever she wore would get soaked and ruined in the process.

So, she designed a special combat outfit made of a material that blocked external impacts or intrusions while allowing for free flow of blood from the inside out. The result was her current bodysuit, optimized for using her abilities.

Honestly, if I had to wear something like that, I’d just buy new clothes every time.

That thought reached the tip of my tongue but stopped there. After all, I’m a guy. For someone like my sister—a beautiful woman—a bodysuit wasn’t bad at all. It actually looked great.

Though she seemed embarrassed, her expression suggesting she’d rather not wear it if she had a choice.

“Hm.”

“Sister.”

“Yes…? What is it? Don’t ask anything embarrassing, okay? I’m already a little flustered.”

“It’s not that.”

“Then what?”

“Don’t show that outfit to any other men.”

“….”

Silence.

My sister’s face turned bright red. Her pale, almost corpse-like complexion flushed so deeply that I was momentarily amazed it could even do that.

She pressed her lips together and stared at me for a moment before, finally—

“…Wh-what are you saying?”

She pretended not to understand.

As if she hadn’t heard every word, with her face burning like that. The act was so blatant that it annoyed me, so I doubled down and raised my voice.

“I said, don’t show that outfit to any other men.”

“Eep!”

My sister flinched at the sound of my voice, seemingly startled. Realizing she couldn’t keep pretending, her eyes darted about nervously.

“…I mean… why…?”

Normally, she would have laughed it off with something like, “You’re so sweet, worrying about me! My little brother is so thoughtful.” But now, her embarrassment only made me bolder.

“Because I’m jealous.”

“…!”

She froze, her face somehow turning an even deeper shade of red. For a moment, she seemed like a kettle about to whistle. I half-worried she might actually explode.

But before this back-and-forth could turn into a comedy routine, I shifted into a combat stance. She might not have been in the right headspace yet, but a preemptive attack would snap her out of it.

“I’m coming.”

“Huh? W-wait, what—?”

Bang!

I fired a 「Burst」-imbued black dot. Instead of using 「Connection」, I generated a barrage of black dots midair and launched them like bullets.

“Ah!”

Finally realizing the seriousness of the situation, my sister quickly covered herself in blood armor and raised a shield of blood to block the explosion.

The dots collided with her shield, bursting in rapid succession. The wide area of the attack caused explosions to ripple across the room. But before the detonations even fully subsided, a dark red figure shot through the smoke and flames.

“You! That’s so underhanded!”

“Who told you to let your guard down?”

Hovering midair with black shadows billowing like wings, my sister steadied herself, a crimson lance of blood and shadow in her hand. It was a perfect synergy of her vampiric blood manipulation and the trait 「Form」, which allowed her to shape magic into tangible weapons and armor.

I could probably replicate some of that, but crafting something as intricate as her armor and lance? No chance. Even if I could, it wouldn’t match her level of refinement.

“Get ready!”

She seemed genuinely annoyed. The magic swirling around her lance was no joke. This sparring match was shaping up to be a one-and-done deal—one hit, and it would be over.

I focused on a black dot forming at my fingertips.

My sister adjusted her stance, preparing to throw her lance. I imbued my black dot with 「Negation」 and continued to concentrate on it.

As the black dot grew larger, swelling to the size of my fist, my sister hurled her lance. At the same moment, I released my black dot.

Boom!

The resulting sound was deafening. I wasn’t sure whether it came from her lance or my black dot. But one thing was certain.

When her lance and my black dot collided, there was no sound at all. Both simply vanished, perfectly negating each other.

“….”

My sister stood there, staring daggers at me, looking thoroughly annoyed and waiting for my next move.