The sea churned, not with its usual restless energy, but with a palpable, primal grief. In the silent, cavernous heart of Kymopoleia’s domain, amidst kelp forests swaying like funeral shrouds and coral reefs stripped of their vibrant hues, the now twins remained. Marin was gone. Swallowed by the abyss, devoured by a primordial wound that bled pure non-existence.

Corina floated, suspended in the water, her eyes vacant, fixed on nothing. Marin, like her siblings had a weapon, she never used it, but it was everything Corina had to remember her, remained clutched loosely in her hand, a relic of a life snuffed out too soon. There was no sound from her, no wail, no sob. Only a terrifying, profound numbness. The secret, their existence as Kymopoleia's mortal-sired children, was out. One third of their precarious trio had vanished, leaving a void that was not just grief, but a chilling premonition of their own fragility. She whispered Marin’s name, a raw, formless sound lost in the desolate water, a desperate prayer that already felt answered in the negative. Fear, cold and sharp as a jagged ice shard, began to mingle with her sorrow, fear not just for herself, but for the brother who now thrashed beside her.

Cyrus was beyond numbness. His grief was a maelstrom, a hurricane confined within his skin. He plunged his own trident into the very bedrock of the seafloor, cracking ancient formations, stirring up blinding clouds of silt. He tore through a patch of luminous anemones, their delicate light extinguishing as if offended by his rage. "They let her die!" he screamed, the sound echoing not with his voice alone, but with a guttural, ancient resonance that vibrated through the water, distorting the very currents around him. "They stood there! The hero and his architect! Useless! Weak!"

Each surge of fury was met with an answering thrum deep within him, a resonance that was not only his own, but seemingly amplified by the wild, untamed chaos that now twisted through his mother's domain, it seemed to find a willing conduit in his shattered heart. It whispered of retribution, not as an option, but as the only path to quiet the screaming void Marin had left. It honed his anger into a razor's edge, sharpening his conviction of Percy and Annabeth's unforgivable guilt. The power itself felt like a hungry thing, feeding on his pain, promising him strength to make them pay.

He remembered Percy Jackson, the son of the sea, who had dared to stand against him. He remembered the architect, Annabeth Chase, whose brilliant mind always found a way. Of course he remembered. Their mother, Kymopoleia, told him, for an unknown reason only to him, about Percy and the plans he made with a roman to build her a temple in New Rome and a Cabin in camp Half-blood after the fight with Gaia, she also told him about Annabeth, the daughter of Athena, retriever of the Athena Parthenos, named the official architect of Olympus and New Rome, —overachiever— his mother called her, but competent nevertheless. 

They took Marin from us, a thought, impossibly clear and cold, formed in his mind. I will take her from him. Not just death, no. That is too quick. Marin had been swallowed, vanished, yet lingering, a ghost in the abyss. Percy should suffer the weight of Annabeth's absence, knowing she was just out of reach, a constant phantom of what he had lost. A perverse logic took root, promising a twisted form of balance. They will know what it means to lose everything.

Corina reached for him, her eyes wide with dawning horror. "Cyrus, no! Marin would never like this! This is...madness!"

He turned, his eyes burning with an unnatural light that dimmed the bioluminescence around them. "Madness is allowing them to walk free while Marin is...gone!" His voice was an oceanic roar, amplified, twisted. He shoved Corina away with a burst of hydrokinetic force, sending her tumbling through the water. He didn't look back. His mind was set, fueled by a grief so profound it had been corrupted into pure, vengeful resolve.

He would find them. And the architect, who saw everything and understood nothing, would be his instrument of vengeance. The surface world beckoned, promising a reckoning.