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

Merlin stood up, the wind clawing at his ragged cloak, his chest still heaving from the fury he had poured into his words.

"Ohhhh… demi-gods," he spat, tasting the venom in his own mouth. His teeth ached from the force of his clench. "That's why I hate them. That's why I hate you. All of you." His voice rose until it seemed to bite at the sky itself.

Them, and their fucking gods.

He hated them with a pure hatred, the kind that gnaws marrow, the kind that rots into bone and cannot be cut out. It wasn't the hatred of envy. It wasn't even vengeance, not fully.

It was purer, colder, sharper: the hatred of something unnatural that had stolen the natural place of humankind.

A flash of memory cracked behind his eyes—blood, his master's blood, soaking the sand of a ruined battlefield. The demi-god had laughed, a laugh that sounded like storm-chimes breaking. Merlin hadn't even been strong enough to scream then; his voice had cracked. He had only watched.

And now—now he stood, scarred by centuries of magic, cursed by the price of learning too much, yet still alive. Alive and spiteful.

The air around him shifted. Not just wind—ozone, sharp and metallic, the tang that precedes lightning.

The demi-god.

Kaelion. That was his name. Merlin knew it the instant his eyes fell on him, as if his hatred had branded the word into his skull years before this meeting.

Kaelion smiled, lips curling with the arrogance of eternity. His voice boomed without effort, carried by some divine resonance.

"You bark loud, mortal." His gaze roamed Merlin as one might survey a rat too bold to scurry. "Hatred suits your kind, though. It is the only crown your frail heads will ever wear."

Merlin's grip on his staff tightened until wood cracked. He did not answer—not yet. Words wasted were blades dulled.

Kaelion walked closer, the ground humming beneath his steps. The air warped with each footfall, thunder's echo in miniature.

"You dared to curse us. You dared to curse the gods themselves. Do you think your tongue makes you mighty? Do you think your scars make you eternal?"

Merlin's lips split into a feral smile. "No," he said, his voice a rasp, low and cutting. "But they make me... human."

The word spat like fire against Kaelion's lightning. For a moment, silence pressed—the weight before a storm. Eli, and Claire holding Lara from taking any action.

Then the storm broke.

Kaelion's hand snapped up, fingers curling as arcs of lightning wove into a spear of raw energy. He hurled it with the contempt of a man flicking away an insect.

Merlin slammed his staff into the earth. Runic sigils flared, jagged and crimson, like wounds cut into the ground. A wall of black fire roared up, swallowing the spear. Lightning and flame clashed, shrieking, burning the air to ash. The explosion tore the ridge apart.

Merlin staggered but stood firm, cloak whipping, eyes burning with the same hatred that had never once dimmed.

"You bleed lightning, another bastard of Thor..." he hissed. "Let's see if it spills red."

Kaelion laughed. Gods, he laughed. The sound was silk over steel. "You amuse me, mortal. Do you want glory? Do you want to be remembered when I carve your corpse into dust?"

Merlin answered with fire.

His staff burned, runes igniting in sequence, and with a guttural roar he unleashed a torrent. It was not clean flame; it was corrupted, twisted by every bargain, every forbidden grimoire he had ever clawed open. Green mixed with black, smoke laced with screams only he could hear.

Kaelion raised his hand and caught it. The demi-god's palm glowed, crackling with arcs, holding back the flame as if he were grasping a rope. Then with a twist of his wrist, he hurled it aside. The fire slammed into the mountainside, carving molten channels into stone.

Merlin's heart pounded—but not with fear. With fury. Fury and exhilaration.

He raised his staff again, whispering words in a tongue that even the damned had forgotten. The sky above darkened, clouds boiling with his call. From the heavens came not rain, but shards of obsidian, jagged knives falling like hail.

Kaelion blurred, his body splitting into lightning. He moved through the storm of stone like a phantom, untouched, appearing before Merlin in less than a heartbeat. His fist slammed into Merlin's chest.

The world shattered.

Merlin flew, bones screaming, slammed into a boulder so hard it split. Pain burned through his ribs; copper filled his mouth. He spat blood, red against grey stone.

Kaelion stalked forward, unhurried. "You fight well. For a worm. But all worms end the same—crushed underfoot."

Merlin coughed, wheezed, but laughed. The sound was cracked, but it was laughter. "If I'm a worm," he said, dragging himself upright, "then watch how a worm bites."

He raised his hand—not the staff, just his bare hand—and drew blood across his palm with his teeth. He slammed that bleeding hand onto the cracked stone.

A sigil erupted—raw, ancient, forbidden. From the earth below, a scream answered. A skeletal hand clawed free, then another. Spirits, bound and furious, rose at Merlin's command, their eyes hollow flames.

Kaelion paused. For the first time, a flicker of distaste crossed his divine face.

"You summon carrion. Pathetic."

"Pathetic enough to bleed you," Merlin spat.

The spirits surged, shrieking, clawing, lashing at Kaelion. Lightning cut them down, one after another, but each strike slowed him, each wail made the air heavier.

Merlin staggered closer, hatred burning brighter than the pain in his ribs. He raised his staff, muttered one last curse, and drove all of his spite into the tip.

The staff struck Kaelion's arm. Not enough to pierce—but enough.

The demi-god hissed as ichor spilled. Blue, luminous, thick. It splattered on the ground, sizzling, burning holes into the stone.

Merlin froze. His eyes locked onto that ichor, that impossible proof.

"You bleed," he whispered. "By the abyss, you bleed."

Kaelion's expression hardened, pride cracking into rage. "Do not mistake a scratch for victory." His voice thundered. "I could kill you a thousand times before you took another breath."

Merlin grinned, blood staining his teeth. "Then do it. Or live forever knowing a human made you bleed."

The demi-god's fist clenched. Lightning flared. For an instant, Merlin thought death had come—clean, final.

But then Kaelion laughed again, sharp and cruel. He turned away. "Slaying you would dishonor me. Worms are not worth gods' wrath."

In a blur of light, he vanished, the storm collapsing with him, leaving only scorched earth and the stink of ozone.

Merlin fell to one knee, coughing blood, ribs shattered, body screaming. But his laughter—raw, jagged, unstoppable—rose into the silent air.

He had seen it. He had made it happen.

A demi-god bled.

And if one could bleed—then one could die.