Sikandar (Alexander the Great) and Porus were two great warriors. When Alexander invaded India, he faced Porus. Porus was a king in the Punjab region. Their battle was fierce. Porus fought bravely with his elephants and army against Alexander's well - trained Macedonian troops. In the end, though Porus was defeated, Alexander was so impressed by his courage that he allowed Porus to continue ruling his kingdom under his suzerainty.
One common theme is self - discovery. Since Zenitsu has a complex personality, many fanfics focus on him finding out more about himself, his powers, and his place in the world. Another theme is friendship. He often forms strong bonds with other characters in fanfics, like Tanjiro and Inosuke.
Definitely not. In the manga, there's no such plotline of Zenitsu and Nezuko getting married. Their relationship is more focused on being comrades in the fight against demons rather than a romantic one leading to marriage.