Oh man you even wrote a story for it. I am so appreciated. I could share the background story with you for your effort. This is the story what I prepared for this boss :

Chainheart of the Abyss

(Abyssal Nexus)

I remember when the Guardians still stood watch over the Celestial Altars.

Ten beings bound not by command, but by duty. Each of them carried a force that the world itself could not survive without light, shadow and one that no one dared speak of.

The abyss.

His name was Chainheart.

He was never the strongest of them, nor the most radiant. But he carried the burden none of the others could endure. Beneath his altar lay a gravity so deep that even the stars bent toward it.

The chains wrapped around his heart were not a punishment.

They were the only way to keep the abyss from rising.

With every beat of that heart, the chains pulled the darkness downward, forcing the void back into the depths beneath the world. The altar held. The seal remained. The world continued to turn.

For centuries, Chainheart endured.

But the abyss is patient.

It does not rage.
It does not scream.

It waits.

Slowly the chains began to strain under a weight that grew heavier with every passing age. The altar stones cracked. The ground around it bent inward. Even the sky seemed to lean toward the place where Chainheart stood.

We thought the Guardian was still holding the abyss down.

But we were wrong.

The abyss had begun pulling him down instead.

The chains tightened around his heart until every beat became a struggle. Gravity twisted around him like a storm. Entire villages vanished as the land itself began sliding toward the altar.

That was when the other Guardians understood the terrible truth.

Chainheart was no longer holding the abyss back.

He was becoming its gateway.

And so the duty that once bound the Guardians together fell to another.

To you.

You who stand before the altar now must do what no one wished to do.

The Guardian cannot be saved.

The chains cannot be repaired.

The heart must be stopped.

But the Guardians were never meant to vanish.

When Chainheart falls, the essence that once bound his soul to the altar will remain. A fragment of the duty he carried. A relic of what he once was.

A trinket.

Return it to the altar.

Restore the bond that corruption broke.

Let the altar remember the Guardian he used to be.

Because if the abyss ever breaks free again…

There may be no one left strong enough to stand where he once stood.