Duryodhana and Karna
Duryodhana (Cambodia, ca. 900s AD)
Duryodhana was the enemy of the Pandavas in the story of the Mahabharata, and he's forced out of power when the Pandavas defeat him. His friend Karna fights for him, defeating many kings, but eventually Arjuna kills Karna in a great battle.
Duryodhana's mother, fearing for his life, uses magic to make him invincible. She can make him invincible just by looking at him, and she looks at every part of his body, but out of modesty he covers his private parts, so they're still not invincible.
Then Duryodhana, grieving for his friend and enraged by his death, kills a great warrior, his enemy Chekitana, before being killed in battle himself, by a below-the-belt blow with a mace. Duryodhana's consolation is that he will be surrounded by friends and family in the afterlife.
(Compare the story of Achilles and Patroclos).
Learn by doing: write a story about a friend who fought for you, or when you lost a friend.
More about the Mahabharata
Savitri: A Tale of Ancient India, by Aaron Shepard (1992). A retelling for kids of one of the more feminist stories in the Mahabharata, with lots of pictures in a traditional Indian style.