when in Sarala’s narrative he knew right from his childhood that he was his brother? Why was he so focused on killing him? In the Kurukshetra War brothers didn’t kill brothers; cousins were the targets. Incidentally in Vyasa Mahabharata too Karna was no less determined to kill Arjuna. It is just that he got to know of his relationship with him in this narrative much later, but still before the War. As is well known, in Vyasa’s version, Arjuna had always been Karna’s target. He hated him. Things had already become far too complicated before he knew that Arjuna was his brother.
In any case, in Sarala Mahabharata Karna’s story is rather different. When they were all small, Kunti herself had introduced her sons to him and told him that they were his younger brothers. She made them prostrate at his feet as younger brothers should do to their eldest brother. Karna was upset that Kunti had given the status of her eldest son to Yudhisthira knowing that he was her second son. The hurt child told his mother that now he would get back his status as her eldest only after killing Yudhisthira. Kunti was distressed and disappointed and left with her three sons (Nakula and Sahadeva were not born yet) but no harsh word was said to Karna by anybody. In any case Arjuna did not figure at all in that exchange between the mother and her eldest son.
Later, Karna, the Pandavas and the Kauravas became guru Drona’s pupils. So was Drona’s son, Aswasthama. King Drupad had sent his sons, Dhristadyumna and Shikhandi (after she became male by the grace of a Yaksa), to Drona for their education. At that time there was no rivalry between Karna and Arjuna. The rivalry, which was really one-sided, was between Aswasthama and Arjuna. Aswasthama was jealous of Arjuna and he resented it strongly that his father imparted knowledge of some very special divine weapons to Arjuna alone. Incidentally Drona had never said that he would make Arjuna the greatest archer, nor had Arjuna ever sought or even expected such a commitment from him.
In Sarala Mahabharata there was no situation – there couldn’t simply be – where Karna was humiliated or discriminated against on account of his caste because everyone knew that he was Kunti’s son. True, he was called “Sutaputra” (roughly, son of a charioteer) but that was because he was brought up by a Suta. He went to Draupadi’s swayambara to win the princess, not for himself, but for Duryodhana and participated in the archery test but failed to hit the target. He was not a party to Draupadi’s humiliation in the Kaurava court. He had no role at all in the first or the second game of dice and the subsequent exile of the Pandavas. He neither encouraged nor discouraged Duryodhana to fight a conclusive war against the Pandavas. He did not play any role in the deliberations when Krishna came to the Kaurava court as Yudhisthira’s emissary. Before the Kurukshetra War, there were battles he had fought against Arjuna and there were battles too when they had fought together against their enemies. But there was never any particular hostility or jealousy, let alone enmity, between them. In fact in the narrative the only example of such lingering enmity fed on intense hatred from time to time was between Bhima and Duryodhana. Karna wished for the Pandavas’ victory in the War and for Yudhisthira to be the king. But he had no intentions of making things easy for him in this respect.
It was another matter that circumstances arose which forced him to do precisely that. On the eve of the War Kunti extracted a promise from him that he would not kill Yudhisthira, Bhima, Nakula and Sahadeva. She said she would accept it if he killed Arjuna or Arjuna killed him. About this promise to his mother Kunti, Karna never told Duryodhana. He honoured it in the battlefield. Although during the War, when he was the Commander-in-Chief of the Kaurava army, he defeated each of the four and could have easily killed them, he did not. The War might have taken a different turn, or at least the situation could have been notably different, had he killed them or even any of them. In any case, his promise to his mother severely narrowed his option in the War; he had to focus on Arjuna and Arjuna alone. He must have persuaded himself, at least after giving his word to his mother, that Arjuna’s death would decide the War against the Pandavas.
But wasn’t he focussed on Arjuna even before his mother extracted that promise from him? Didn’t he collect divine weapons to kill Arjuna specifically? As far as I can recollect (the text is not with me right now) it was not really so in Sarala Mahabharata. However, granted for the sake of argument that it was indeed so; is there anything surprising? On the Pandava side only Arjuna had divine weapons. Karna being an honourable man, would he have attacked his other four brothers or Drupada and his sons or Virata and his sons with divine weapons? The only one he could have used them against was Arjuna!
He was committed to Duryodhana. They were friends from childhood. As mentioned earlier, Kunti’s visit to him when she told him that he was her eldest born and introduced her sons to him did not end in a pleasant note and in any case it was a bit too late for forging emotional bonds between him and his brothers. He did not grow up with them. His mother did not take him with her but left him in Radha’s house when she went back after that visit. When Duryodhana became king, he became one of his key advisers. When he went to war against the Pandavas, Karna knew that he depended on him. Karna was an honest person, a virtuous person. He fought most sincerely for his friend to win.