Sure, here's the translation in casual English:
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Alexander woke up and looked in the mirror. After a sharp look at his appearance, he said, "Huh, black hair, a light body, and over 175 cm tall? It looks like me from my past life. The difference is this body is incredibly weak; even a child could hurt it." Alexander sighed, and then someone knocked on the door. Leonard asked, "Sir, may I come in?" Alexander replied, "Yes, come in."
Leonard entered with a huge bundle of important papers and said, "These are all the documents you might want to know about, sir." Alexander took the papers and allowed Leonard to leave. "Alright, let's see what I need to know about my new life..."
After two days of reading the documents, which exhausted Alexander, he understood everything he needed to know. He realized that his father was a duke, not a marquis, but his father belonged to the Crimson Bird Empire, which was hostile to the Winter Dragon Empire. As the name suggests, the Crimson Bird Empire, also known as the "Fire" Empire, only uses the fire element.
In contrast, the Winter Dragon Empire, known as the "Winter" Empire, uses the ice element. Alexander's father, Duke Marcus, was from the Marcus Duchy, one of the strongest duchies at the time. He was a brave warrior who feared no one. He had an army of over half a million soldiers and thousands of first-rank grand wizards and peak first-rank leaders, and he himself was at the peak of the second rank.
But he had a dangerous secret: he could use two elements at once, ice and fire. Alexander's father didn't want to reveal this secret because it would make both empires ally against him. According to an ancient manuscript, it was foretold that someone would appear to stop the centuries-long war between the two empires and unite them under one banner.
Both the Fire Emperor and the Ice Emperor feared this prophecy, and anyone who showed this rare ability was killed immediately. Duke Marcus kept this secret until it was revealed by the most unexpected person, his brother Gabriel, the current marquis.
Gabriel informed the Fire Emperor immediately, and the Fire Emperor declared Duke Marcus a traitor. The duchies that hated Duke Marcus and coveted the Marcus Duchy, one of the four largest duchies in the empire, allied against him.
Despite Duke Marcus's strength, his army of 100,000 soldiers couldn't withstand over half a million soldiers and four duchies, each at the peak of the second rank. Despite the duchies' struggles, Duke Marcus's fate was sealed after thousands of his aides and soldiers betrayed him. He could no longer look up at the sky until he stood up, his face covered in blood. Everyone left on the battlefield feared this man's ferocity and terrifying techniques, which allowed him to withstand over half a million soldiers. Silence filled the air until one of the four duchy leaders spoke, "Surrender, Marcus, and I promise your young son, whose mother died during childbirth, will be safe."
Marcus looked silently and laughed loudly, scaring the four duchies. He then said, "Do you think I'll believe that? I bet that after my death, you'll kill even the children and women in the duchy."
Marcus drew his sword, called the Phoenix Sword, which the emperor had given him for his achievements against the Winter Empire, and said, "I promised not to draw this sword as long as the empire wasn't in danger. Here, I give you this sword because I won't break my promise even if I die." He threw the sword and took an ordinary sword from the ground, saying, "Anyone who wants to touch the Marcus Duchy must walk over my dead body first."
The duchies prepared for a full-scale attack on Marcus until a deadly aura suddenly swept across the battlefield. Even the four duchy leaders fell to the ground from the sheer power of this aura. Only one person in the Fire Empire possessed this aura, the emperor himself. The battle between the two armies stopped in the emperor's presence. If you moved an inch, you'd be wiped off the face of the earth.
The emperor looked at Marcus and said, "Marcus, my dear friend, I never expected we'd end up fighting each other as enemies." Marcus stared at the emperor and said, "Rex, I didn't expect that after helping you take the throne, you'd do this to me. Is this how you reward my loyalty? Did you really think I wanted to take the throne from you?"
The Fire Emperor laughed lightly and said, "I know you don't want the throne, Marcus, but I won't let anyone threaten my throne, not even after a thousand years. Now, how about surrendering peacefully?" Duke Marcus replied, "And then what? You kill my son because he'll be a threat to you in the future?"
The Fire Emperor said, "Based on our friendship, I swear in front of everyone here and in front of ---
And this is my oath that I will not touch your son. Also, we already know that his talent is weak. Even if it turns out he possesses both fire and ice elements, no one will harm him, and he won't even reach the second level. So, I promise I won't touch him."
Marcus looked at his soldiers and saw that only a few thousand remained, even his aides had perished. He then said, "Alright, but promise me also that you won't harm any of my soldiers or the people in the villages and towns owned by my family." Rex replied, "I promise." Marcus raised his sword to the sky and said, "I hope you forgive me, my son, for I was not a good father." Then Marcus stabbed his heart and died standing, looking at the sky.
The emperor ordered Marcus to be buried and deprived his son of the Marcus estate, dividing it among the four duchies involved in the war. The emperor promised Gabriel that he would take charge of the only remaining castle and be appointed as its marquis. Gabriel couldn't oppose, so he agreed and took the castle and some small villages around it with an army of no more than 10,000 soldiers and 1,000 knights.
Marquis Gabriel oppressed Marcus's son, Alexander, at every opportunity. He couldn't kill him because he knew that the remaining soldiers of his father would immediately turn against him, and the emperor had warned him not to kill Alexander until he turned 25, to become fully grown and gain some strength, as he had promised his father.