Starting from Zero to Build a Demon Family
Chapter 10 - Little Cat—Senpai, I Want to Learn Street Fighter!

Chapter 10: Little Cat—Senpai, I Want to Learn Street Fighter!

In the late afternoon, as the sun dipped low over Kuoh Town, the atmosphere inside the occult research club was heavy with residual magic. The faint scent of ozone lingered in the air, still clinging to the floor and walls from the thunderous spell unleashed earlier.

Magic replenishment—among demons, it was known as a method of restoring lost magical energy through the exchange of bodily fluids. To many, it was intimate. To a master and their subordinates, it was sometimes even a reward.

“So… that’s why you stuck out your tongue?”

Kasumigaoka Utaha’s eyelashes trembled. Her cheeks burned with color, and her lips pressed tightly together. Those crimson eyes wavered between Lynn’s face and the window behind him, unable—or unwilling—to settle.

“For maximum replenishment effect,” Lynn answered, full of conviction. He was entirely serious. This wasn’t just flirting. He was genuinely focused on restoring her mana.

The only issue? Utaha had expended so much magic that the replenishment had gotten a bit… intense.

“Ara ara… unexpectedly pure,” Himejima Akeno mused from the side, narrowing her eyes in amusement as a teasing smile tugged at her lips.

Kasumigaoka Utaha’s shoulders twitched.

She had been so caught up in Lynn—his presence, his warmth, his eyes—that she’d completely forgotten others were in the room.

No. No, no, no. Don’t tell me they saw everything? Her heart lurched. That’s social death! Actual, permanent, soul-crushing social death!

Trying to maintain some shred of dignity, she took a deep breath and crushed her panic down. On the outside, she remained composed. But inside, her heart beat like it was trying to punch its way out of her ribs.

She cast a furtive glance at Lynn and muttered under her breath, “That was my first kiss… and he got it for free.”

“How is she?” Rias asked, walking over with concern. “Has Kasumigaoka-san recovered?”

“I think… I’m okay?” Utaha smiled awkwardly, unsure of how to act under the weight of all this attention.

Rias studied her for a moment, then gave a knowing grin. “It seems Lynn’s magic replenishment was quite effective.”

Utaha’s smile froze.

Seriously, could she not bring that up again?

Rias, meanwhile, looked genuinely impressed. “I didn’t expect Kasumigaoka-san to be able to handle super-tier magic so quickly. That’s an incredible talent.”

Just that one spell—if fully developed—showed immense potential. With enough growth, she could easily rival Akeno in raw power. Rias couldn’t help but feel a little envious.

Hearing that, Utaha finally remembered what she had done before collapsing. Her eyes turned toward the scorched crater on the training grounds, still smoldering faintly beneath the twilight sky.

“Although it was powerful, I still feel like it was missing something,” she murmured, gaze fixed on the damage.

That was why she had poured every drop of her magic into the strike. All or nothing.

“Naturally,” Akeno replied. As a thunder magic specialist, she stepped forward with calm authority. “When released at full power, Lightning Strike can influence the weather itself. With your current mana levels, you’re still far from drawing out its full potential.”

“I see…” Utaha nodded slowly, her expression thoughtful.

Even if it was high-level magic and well-executed, she hadn’t truly unleashed it yet.

But then again… maybe that was enough—for now.

Lynn raised his index finger, and a sliver of black lightning danced across it like a living snake. The moment Utaha’s spell had been recorded in her demon grimoire, Lynn had absorbed and mastered it in silence.

For a high-ranking demon like him, lightning magic was a versatile tool. And this particular technique? It was a silent thunderbolt—soundless, traceless.

No one present noticed the spell take form.

No one, except…

Akeno’s eyes widened. Her gaze locked on the flicker of black lightning at Lynn’s fingertip, a sharp chill running down her spine.

That energy… it felt like Rias’s magic. Lightning infused with a destructive force.

Lynn caught her eye and offered a small smile before gently curling his fingers, dissipating the spell like it had never existed.

Akeno returned the smile, but inside, her thoughts churned restlessly.

Black lightning. Undeniably Lightning Strike, yet altered. The color didn’t surprise her—her own unique bloodline had given her lightning a strange hue too. But what troubled her was how casually Lynn had displayed such mastery.

He only glanced at the scroll… right? Then why did it feel like he could cast the spell better than she could?

His control just now—she couldn’t replicate that even at her best.

Lynn Walburga.

The last heir of the Walburga bloodline. Definitely not a simple man.

On the other side of the room, Rias let out a soft sigh. “Such a shame. Even with a super-tier spell, we still couldn’t push Kasumigaoka-san to her limit.”

Lynn chuckled. “If you ever want to test further, Rias-san, just give me a call.”

She rolled her eyes. “No thanks. We already used up one super spell for this. Who knows what it’ll cost next time?”

“Tch, what a pity.” Lynn shook his head, looking exaggeratedly disappointed.

But he didn’t believe for a second that a noble house like the Gremorys would run out of resources so easily. Especially not when Rias’s brother was a demon king with transcendent power. There were bound to be treasures they hadn’t yet shown.

Satisfied with today’s results, Lynn made preparations to leave. Before they parted ways, Rias asked Koneko Toujou to show them around Kuoh Town for a bit.

Evening had fully arrived when they ended up at a local arcade.

“So why are we at an arcade again?” Utaha asked, exasperated as she watched Lynn and Koneko locked in a heated game.

“K.O.!”

“Defeated again,” Koneko muttered, staring blankly at her fallen character on the screen.

“Senpai, you’re really strong.” Her tone was flat as ever, but Lynn could tell she meant it.

Utaha glanced at her watch. Her right leg began to bounce. “Aren’t we done yet? If we don’t leave soon, we’ll miss the bus.”

“True.” Lynn reluctantly set the controller down. Though he’d already learned ‘Teleportation via Magic Circles,’ he hadn’t yet marked his home with coordinates, so public transport it was.

“We’ll meet again next time, Koneko.”

“Senpai.” She tugged at his sleeve and pulled out a small flyer. “Please take this.”

He glanced at it. A demon summoning contract. Personal. With her name on it.

“Senpai, I want to learn martial arts.”

Koneko looked up at him, eyes brimming with determination.

Lynn blinked, then followed her gaze to the Street Fighter machine.

Ohhh. That kind of martial arts.

“Sure. If you’re free, come by my place sometime.”

As they left the arcade behind, Utaha crossed her arms and trailed behind Lynn, her gaze narrowed.

“You called her ‘Koneko,’ huh.”

Lynn gave her a puzzled look. “Why do I get the feeling someone’s a little jealous?”

“Hah? Me? Jealous?” She started to deny it, but then her mind blanked out for a moment. She stopped walking, frozen mid-step.

Wait. I am jealous.

She looked at Lynn, emotions twisting behind her eyes. Her gaze drifted unconsciously to his lips.

This is bad. I think I’m falling in love with him…

But we’ve only known each other for two days!

Her thoughts raced through every moment they’d spent together. Her mind finally halted on the scene of magic replenishment earlier, and her heart skipped hard against her ribs.

Lynn had paused ahead, waiting. “Why’d you stop?”

Utaha blinked back into focus, brushed a hand through her windblown hair, and hurried to catch up. Grabbing Lynn’s arm, she looked up at him and whispered, “I admit… I’m a little jealous.”

Lynn blinked in surprise, then let out a laugh. “Better learn to manage that. I’m a demon planning to build a harem, after all.”

“You really are a lust demon, huh?”