The giant was silent for a moment, then said, "To gain this power, you must pass my test. If you fail, you will remain here forever."

Mo Xi and Mu Li looked at each other and saw determination in each other's eyes. No matter how difficult the test was, they would not back down.

The giant waved his hand, and the scene around them instantly changed. They found themselves in a barren desert, under a blazing sun, the heat unbearable. Suddenly, a swarm of sandworms emerged from the ground and pounced upon them. These sandworms were enormous, covered in sharp spines, and moved at breakneck speed.

Mo Xi and Mu Li quickly stood back to back, ready to fight. Mo Xi swung the Pluto Sword, each strike carrying a powerful force, cutting the approaching sandworm into two pieces.

Mu Li used the power of the ancient goddess to cast a protective barrier around them to resist the sandworm's attack. At the same time, she looked for the sandworm's weakness, and when the opportunity arose, she sent out a stream of light, hitting the sandworm's softest abdomen.

After a hard-fought battle, they finally repelled the sandworms. However, before they could catch their breath, the sky suddenly became overcast with dark clouds and lightning flashed. The giant's voice rang out again: "This is just the beginning. Are you ready?"

Mo Xi held Mu Li's hand tightly and said loudly: "Ali, don't be afraid, we will definitely pass the test!"

In the following trials, they faced various difficulties and dangers, including freezing cold glaciers, poisonous swamps, and bewildering illusions. But no matter what they encountered, Mo Xi and Mu Li always supported each other and never left each other.

Finally, they passed all the tests. The giant looked at them with a hint of approval in his eyes: "I am moved by your emotions and courage. I will give you this power. I hope you can protect the Three Realms."

With that, the giant transformed into a beam of light and merged into the bodies of Mo Xi and Mu Li. They felt a powerful and pure force flowing through their bodies, a force that seemed to fill all the holes in the seal, preventing the evil from ever breaking through.

With this power, Mo Xi and Mu Li returned to the sealed area. They cast another spell, fusing this power with the three previous powers. An unprecedented light erupted from the seal. After the light dissipated, the seal became indestructible, and the previous fluctuations disappeared.

Back at the Pluto Palace, Mo Xi and Mu Li finally breathed a sigh of relief. After going through so much, their relationship had deepened, and the underworld had once again returned to peace.

On a quiet night, Mo Xi and Mu Li stood side by side on the roof of Pluto's Palace, gazing up at the unique starry sky of the underworld. Mo Xi gently put his arm around Mu Li's shoulders and said, "Ali, no matter what we encounter in the future, we will face it together."

Mu Li smiled and nodded: "Well, Brother Mo Xi, as long as you are by my side, I am not afraid of anything."

Their figures nestled together under the starry sky, and that scene seemed to have become the most eternal and beautiful scenery in the underworld, bearing witness to their story of love and protection, which continued to spread in this mysterious land...