The Heroine is My Stepsister, and I'm her Final Boss

The night had not yet healed from Kaelion's storm. Smoke drifted in ragged curtains across the ruined ridge, rocks still glowing from the lightning strikes, the stench of ozone sharp enough to burn the lungs.

Merlin crouched amid the rubble, blood dripping from his lips, fingers still smeared with blue ichor. He traced that ichor onto his chest like a rune, a war mark. Every breath hurt, his ribs screaming, but pain had become an old friend—one he knew how to wield.

The demi-god had left, but the sky still whispered with his presence, like thunder unwilling to depart.

"Not gone," Merlin muttered to himself. "Never gone. He'll circle back. Arrogance always does."

And he was right.

The air hummed again. Sparks crawled along shattered stone. A shape rippled back into existence—Kaelion, unbowed, unshaken, fury burning behind his silver hair. His arm, still seared where Merlin's staff had struck, glowed faintly blue. His pride demanded blood.

"I thought you amusing," Kaelion said coldly, lightning crawling over his skin. "Now I think you intolerable. You are not fit to crawl beneath my gaze."

Merlin raised his staff, barely able to stand but refusing to kneel. "Then stop staring," he croaked, "and end it."

But before Kaelion could strike—another voice cut through the scorched air.

"Not while I breathe."

The sound was sharp, young, defiant.

From the haze stepped a girl with hair like a streak of sky, blue falling in waves down her shoulders, eyes burning like twin flames of sapphire. She was young—too young to stand against a demi-god—but her presence carried weight, as though fate itself leaned on her shoulders.

Lara.

Her boots crunched on shattered stone as she walked forward, a short spear in her grip, its tip glinting like star-metal. She glanced at Merlin, and for the first time in ages, the old sorcerer saw something in another's eyes that wasn't fear.

"Old man," she said with a half-grin, "you look like you've seen better days."

Merlin chuckled, coughing blood. "And you look like you haven't seen enough to be this stupid."

Her grin sharpened. "Then watch and learn."

Kaelion tilted his head, studying her as one might study a curious insect. "Another came to die....You breed like maggots. Do you truly believe your youth and painted hair will shield you?"

Lara raised her spear, unshaken. "No. But it will pierce you."

Kaelion's laugh thundered across the ridge. Lightning flared around him—only to suddenly falter. His pupils dilated, his posture swayed for a heartbeat.

From the shadows at the ridge's edge, a new voice whispered, low and smooth.

"Sleep, godling. Sleep."

Claire had arrived. Her violet robes shimmered faintly with runes, her hands raised as spirals of purple light coiled around her fingers. Her eyes, glowing with amethyst flame, locked on Kaelion's. Each word she breathed carried hooks, weaving into his mind.

Merlin felt the air bend with it, thick and sweet like incense. Hypnosis. Not enough to chain a god, but enough to stagger him, enough to slip between arrogance and focus.

Kaelion snarled, shaking his head, lightning bursting to shred the illusions. "Witch—!"

But before he could finish, steel rang.

A blur of silver shot past him, a strike aimed for his throat.

Eli.

Her blade, long and curved, gleamed with precision. She moved with the economy of a predator—no wasted motion, no cry, just lethal intent. The edge kissed Kaelion's neck, sparks flying as divine skin clashed against sharpened steel.

Kaelion recoiled, more out of surprise than pain, but the moment was enough.

Merlin forced himself upright, staff raised. "Three against one," he wheezed, "and still you strut. Tell me, godling—how much pride will you have left when these women carve you apart?"

Kaelion's eyes burned. "You test divinity with insects. Then die together."

The storm broke again.

Lightning roared from Kaelion's body, arcs sweeping in every direction. Rocks shattered, trees split to ash. Lara rolled forward, spear spinning, deflecting a bolt with the shaft.

Eli cut another in half with a single swipe, sparks hissing as her blade screamed. Claire stumbled back, hands raised, purple shields blooming like glass walls. Each bolt cracked them, splintering, but held long enough for her whispers to keep clawing at Kaelion's focus.

Merlin gritted his teeth, forced his staff into the ground, and muttered words that burned his throat. Black fire rose again, this time circling the four mortals like a ward, feeding on his blood for strength.

Lara leapt, spear blazing with blue light. She struck Kaelion's chest, sparks exploding. The demi-god staggered, eyes narrowing.

"A child's toy," he hissed, grabbing the spear with one glowing hand. He yanked her closer, lightning crawling toward her skin.

But Eli was already there. She moved with the swiftness of a blade drawn from its sheath, her sword slashing across Kaelion's forearm. Divine ichor spilled again, sizzling, forcing him to release Lara with a growl.

Claire's voice surged, hypnotic tones wrapping around his fury. "Fall. Fall."

For an instant—just an instant—Kaelion's eyes dimmed, his grip slackening.

Merlin seized it.

He roared a curse and thrust his staff. Black chains of fire erupted from the earth, coiling around Kaelion's limbs, binding him in a prison of flame and blood.

The demi-god screamed—not in pain, but in rage. Lightning lashed against the chains, cracking them, but for the first time he strained. For the first time, he looked contained.

The four mortals stood around him—Merlin bleeding but unbowed, Lara's spear glowing, Eli's blade raised, Claire's eyes burning violet.

"Look at you," Merlin spat, his voice hoarse but triumphant. "The mighty Kaelion, bastard son of Thor, shackled by mortals. Do you feel it yet? That fear? That doubt?"

Kaelion thrashed, fury blazing. "I am eternal! You are dust!"

"Then remember this," Lara said, stepping close, spear tip inches from his throat. Her young voice rang louder than thunder. "Eternal things can still break."

The chains cracked. Kaelion roared. The storm flared brighter, brighter—

And then, with a sound like the world splitting, the chains shattered.

The explosion hurled them all back—Merlin slammed into stone, Eli rolled across rubble, Claire hit the ground gasping, her hypnosis broken. Lara skidded to her knees, spear sparking from the backlash.

Kaelion stood in the center, breathing hard now, ichor dripping from his wounds. His divinity still blazed, but his pride was cracked.

"You will regret this," he thundered. "I will burn kingdoms for this insult. I will salt your names from history."

He blurred into lightning, vanishing into the sky. The storm peeled back, leaving only silence and ruin.

For a long moment, none of them moved.

Then Lara pushed herself up, panting, but smiling faintly. "So… was that good enough, old man?"

Merlin laughed, broken and bitter but real. "Girl… you've got more stupidity than sense." He looked at all three of them—Lara with her fire, Eli with her sword still steady despite the tremor in her hands, Claire wiping blood from her lips but still upright.

And for the first time in centuries, Merlin felt something foreign.

Not hatred.

Hope.

[Fate is looking at you. Lara.]