The Celestial Key in their possession, The Survivors continued their journey, the weight of their cosmic responsibilities never far from their thoughts. With each artifact they acquired, they inched closer to confronting the overlords and unveiling the cosmic truths that connected their world to the universe.

Their path led them to the heart of an ancient forest, where they discovered an ancient tree of immense proportions—a living relic from a time when their world was closely attuned to the cosmic forces. It was said that the final artifact, the Tree of Memories, lay hidden within the heart of this colossal tree.

The Survivors approached the tree with a sense of reverence, its towering branches reaching for the heavens and its bark etched with symbols of cosmic significance. At its base, they found an opening—a portal that led deep into the tree's core.

As they ventured inside, guided by the wisdom of the Celestial Key, they were enveloped in a world of shimmering memories—a place where echoes of the past resided, waiting to be unveiled.

Ealdred, ever the leader, spoke with determination. "This is the final artifact, the Tree of Memories. It may hold the key to unlocking the cosmic truths we seek and the secrets of the overlords who have plagued our world."

Lirael, with her archer's intuition, noticed that the tree's interior was adorned with intricate carvings and inscriptions—a visual history of their world's connection to the cosmos. "Let's start by deciphering these carvings. They may reveal the cosmic events that have shaped our world."

Thoren, his warrior instincts sharp, examined the portal through which they had entered. "This portal represents a journey through time. It may allow us to witness the past events that have led us to this moment."

Selene, with her gift of empathy, reached out to touch the tree's bark, connecting with the living memories it held. "I can sense the echoes of the past, the emotions and experiences of those who have come before us. We must tread carefully and choose our memories wisely."

Corin, the master mage, channeled his magical abilities to sense the energy patterns within the tree. "The Tree of Memories is attuned to the cosmic energies of our world. It may reveal the cosmic events that have shaped our destiny."

As they explored the tree's interior, they came upon a chamber bathed in a soft, ethereal light. At its center stood a crystal pedestal, upon which rested the final artifact—the Tree of Memories in the form of a shimmering crystal leaf.

Ealdred, his heart filled with anticipation, reached for the crystal leaf. As his fingers made contact, the memories of their world began to unfold before their eyes—a cosmic tapestry woven with threads of fate and destiny.

They witnessed the echoes of their world's past—a time when their world was in harmony with the cosmos, a time when cosmic gateways were open, and the power of the universe flowed freely.

But they also saw the moment when the overlords had risen to power, a time when the cosmic balance was disrupted, and their world fell into darkness. The overlords had harnessed the power of the cosmic artifacts for their own gain, leading to the suffering and destruction that had brought The Survivors together.

As the memories unfolded, they saw glimpses of their own pasts—the tragedies, the losses, and the moments of resilience that had shaped them into Survivors.

And then, in a moment of revelation, they witnessed the cosmic event on the night of Ealdred's parents' death—a convergence of cosmic forces that had bathed their world in radiant energy, drawing the attention of the spacefaring civilization.

With a sense of awe and realization, Ealdred spoke the words etched into the crystal leaf. "The past has been unveiled, and the echoes of our world's history have spoken to us."

As he did, the Tree of Memories resonated with cosmic energy, and the chamber filled with a luminous glow. The echoes of the past merged with the knowledge they had acquired from the artifacts and the guidance of the sentient Celestial Key.

The Survivors now understood the true nature of their world's cosmic connection, the origins of the overlords' power, and the cosmic forces that had chosen them for their cosmic journey.

But with this understanding came a newfound sense of purpose—to confront the overlords, restore the cosmic balance, and protect the harmony of the universe.

As they left the Tree of Memories, artifacts in hand and cosmic revelations in their hearts, they knew that their journey was far from over. The overlords remained a looming threat, their secrets waiting to be unveiled, and the cosmic forces that had chosen them watched with anticipation.

But now, armed with the knowledge of the past, they were ready to embrace their cosmic destiny with renewed determination and unity. Their journey had been an odyssey of self-discovery, cosmic revelations, and the unraveling of the mysteries that connected their world to the universe itself.

And as they ventured into the unknown, the anticipation of what lay ahead filled their hearts. The arc of their quest had come full circle, and the echoes of the past had paved the way for the final confrontation with the overlords and the unveiling of the ultimate cosmic truth.

Their journey was not just a quest for vengeance; it was a cosmic odyssey that would shape the fate of their world and the universe beyond—a journey of Survivors chosen by destiny to protect the balance of the cosmos.