Karna reached patal with his chariot within three days. Upon arriving he saw a large army was there, Nivatkavacha seems like they were preparing to attack the swarglok. He was surprised to see the number were double than what devs were expecting. There not ounce of fear in him. He stopped his chariot at some distance with the enemies but in front of them. He left the Charioteer seat and jumped on rathi place to fight. He took out his ordinary bow and plucked it's string which produces a boom sound.
Nivatkavacha rakshaks turned their attention towards the sound and saw a single Chariot standing at some distance and one person on it. He didn't have a Charioteer with him. He didn't seem like dev, asur, yaks, nag etc so he can be human only. They thought he must be someone who, Dev's in swarglok has sent to stall them. They thought of it as insult that enemies havr sent only one person. It was naked provocation to them. Due to their boon nobody has dared to challenge them in all these years and now a petty human dare to come here and provoke them. There was no leader among them as they were all similar in everything looks, strength, intelligence etc. They thought of making an example out of this human. They will kill him painfully and present his head first thing when they reached swarg.
The army gathered to kill him and shot arrows towards Karna that fully covered the sky, the wanted to finish him as soon as possible and Start their victory march from here only. Karna saw these arrows and fired agneyastra which destroyed the arrows. Seeing this Nivatkavacha began to shoot their weapons at Chariot to destroy the chariot. Karna fire vayuastra and dispersed the coming weapons. Nivatkavacha became angry and decided to fight seriously and they covered everything with illusions but being student of Bhagwan Parshuram Karna was never reliant on his eyes, he was trained to fight with all his senses and even relying on intuition. So these didn't became obstacles for him. Like this a destructive war started in patal lok. Karna alone fought all the rakshaks with his ordinary bow and started killing them all. Being a archer only below lord Shiva, his valour was clearly shown. He killed the enemies with various divyastras. He even used Brahmastra and Bhargavastra to destroy two third of Nivatkavacha's army present there. The rakshaks saw this and decided to disperse and attack karna with huge rocks. Karna destroyed the rocks sent towards him. The battle went on for five days continuously and in the end Karna killed each and every Nivatkavacha in patal but as finished them he saw a flying palace came there.
They were none other than the comrades of Nivatkavacha the polom rakshas who alos planed to attach Swarg. They have gotten flying castle and city from Brahamdev because of the penance of late princes of polom rakshas dynasty. They arrived here with their army at decided time according to their agreement. Since they live in flying city the didn't feel the quakes which happened due to battle. They arrived and saw their partners were dead. They became angry and come down with thousands of Chariot that marched towards Karna to kill him. Karna on the other hand was glad that he didn't have to search for them. He was well aware of them and their City, Parshuram has told him about every formidable Dev's, asur, rakshaks, yaksh, nag ,gandharv etc when he was studying under him.
Karna once again raised his bows and started fighting. The polom were more formidable than Nivatkavacha because unlike Nivatkavacha they have a king who was guiding his army but their efforts were in vain. Karna whose body and mind was of Vajra wasn't even breathing hard after five days of battle. He started firing arrows at upcoming enemies be it foot soldiers, Chariot or elephant riders. The difficult battle took place. After three days Karna killed four fifth of polom rakshaks. Seeing that they were going to loose the polom under the guidance of their King Kalkey. They returned to city to lift it off and run away. The city was going to fly away but Karna fired four different divyastra surrounding it making their escape plan to fail. Seeing that there was no escape the polom rakshaks and Kalkey stated throwing down their weapons from a height towards Karna. Karna countered every thing and killed every last of poloms now only their King Kalkey was left. Seeing everything Kalkey brought his city down came towards battle field.
Kalkey : I am king of polom Rakshaks Kalkey. Who are you and why have you came here and killed all Nivatkavacha and my people?
Karna : My name is Radhey Karna. I am Parshuram shishya. My gurudev had told me to kill Nivatkavacha and polom on request of Devraj Indra because you were misusing your boons and was going to attack swarglok.
Kalkey : You have killed everyone in my city, but if you want to kill me. I challenge you to have duel with me and kill me without using archery or your teacher have only taught you archery.
It was his last trick as he knew he couldn't escape from him and Fighting Archery with him was akin to suicide. He alone has killed nearly 13 million rakshaks with a bow which has nothing divine about it and he didn't have a scratch or sign of weapon hitting him despite of not wearing any armour on his body. He banked on his immense physical strength and fatigue of Karna after constant battle of successive days.
Karna (angrily) : I know you are doing this purposely because you are afraid of my archery but you should not have insulted my gurudev. Fine I will show you what all my gurudev taught me.
Karna became angry at Kalkey for questioning Bhagwan Parshuram. He who was ready to fire arrow at Kalkey suddenly because of anger pulled the string of bow with his all strength resulting it to snap from the middle. Due to his suddenly increased strength he was not able to properly use his weapons at they felt too light for him. He was actually not fighting with his complete strength. He accepted the duel and came down his chariot.
Karna picked up mace while Kalkey was dual wielding swords. Both fighters clashed with each other. Kalkey was shocked getting overpowered bu mere human as Rakshas naturally has greater strength than humans and he had great strength even compared to other rakshas. They both faught with each other but Karna easily defeated and disarmed Kalkey and he killed him by smashing the head of Kalkey. Like this task given by Bhagwan Parshuram to karna was completed after 8 days of continuous fight. Karna then burner all the rakshaks and did their final rites and prayed for better afterlife for them.
There was one eye who has watched everything. It belong to none other than Asurguru Shukracharya. Patal was natural habitat of Asurs. But these Nivatkavacha and polom killed the asurs here and avquired whole patal. This was the reason Asur were force to leave and live on prithvi lok. Shukracharya never left patal. Like Bhagwan Parshuram shukracharya too decided to not to teach any asurs after his repeated failures so he just stayed in patal and penanced Lord Shiva. So the rakshaks didn't dare to disturb him and left him alone. 8 days ago he felt the disturbance in patal and come to see what and who was causing the disturbance. When he came here he saw a young man in his early twenties was fighting the all the Nivatkavacha alone and he was killing them. Since he knew of boon he understood that the young man was human. He saw everything and was amazed by skills and abilities of him. He saw entire battle and Young man has killed everyone without getting hit even after nce. The Archery of the young man was some he has never seen in any other person. He knew most of entities create by tridevs but he never saw such Archer in three lok. He was surprised when young man introduced himself as Radhey Karna and students of Bhagwan Parshuram no wonder he was such great warrior. He was surprised when Karna bow snapped. He had doubts that the young man was not using his full strength as he looked slightly uncomfortable but nbthe beginning but at that time he chucked that as nervousness but now he was sure of it. He was once amazed by his physical strength when he fought Kalkey. He was shocked that Karna even performed the last rites of Rakshas. He was truly impressed by his valour, strength, and humility. He decided to come and talk to him.
Karna who just finished last rites of Rakshas turned around to see a person with only right eyes was standing behind with a stick inbhis hand. He recognised him and immediately folded his hands and bowed down to touch his feet.
Karna : Pranipat Asurguru shukracharya.
Shukracharya (surprised) : Kalyan ho. You recognised me?
Karna : How can I not recognise you. You are also a great devotee of Mahadev like mu Gurudev. He has told me about you and said to show you same respect as I have for him.
Shukracharya (smiles) : Sadho Putra. I am very impressed by you. You have freed patal from these Rakshaks. Ask me something if possible I will give it to you.
Karna : There is no need of that. I just did what guru asked. Your blessings is enough for me.
Shukracharya (smiles) : Bhagwan Parshuram is lucky to have such student.
Karna : No, I am lucky to have him as my teacher.
Shukracharya : Able teacher will make great student, that is true Putra but not every teacher get able students. You don't want anything but I want to give it to you. Ask something.
Karna was going to deny but suddenly indradev came there. Indradev and others Dev's were watching the battle of Karna and Rakshaks as results of this battle will decide their fate. They too were impressed and decided to reward Karna once he come to swarglok as decided by Bhagwan Parshuram to learn from Devguru brihaspati. When Shukracharya came there and told Karna to ask anything they were pleasantly surprised. Indradev decided to use this opportunity. As Bhagwan Parshuram wanted karna to become king and there is no better teacher of politics than shukracharya so he came down to help in that endevor.
Indradev : Pranipat Asurguru.
Shukracharya : Pranipat Devraj.
Karna : Pranipat Indradev.
Indradev : Shukracharya you want to give karna something then accept him as your student.
Shukracharya : He is well trained, what else could I teach him.
Karna : Yes Devraj. I have my Gurudev.
Indradev : Putra, Karna you didn't knew but after you left from Mahendragiri, Bhagwan Parshuram wanted me to bring you to swarg to study under Gurudev brihaspati about how to be a king. Bhagwan Parshuram has trained you to warrior but other skills are needed and there is no better teacher than shukracharya for politics. Learn from him after that I will take you to swarg.
Karna became silent hearing what indradev has told him. Bhagwan Parshuram orders were absolute for him so he will obey his words and If shukracharya decided to accept him as disciple he will learn from whatever he will teach him. Shukracharya was silent because it was big decision to accept Karna as his disciple. He was impressed by him and wanted to take him as deciple but he was already student of Bhagwan Parshuram so he let go of his thoughts but now the opportunity have presented itself. He saw how much Karna respected Parshuram, he will be happy to receive such student. He was also longing for such stude He didn't mind sharing deciple with Bhagwan Parshuram and Devguru brihaspati.
Shukracharya : So, Putra Karna do you want to be my student.
Karna : Yes, please accept me as your student.
Shukracharya (seriously) : Fine I accept you as my student But I want complete devotion and I wouldn't teach you anything else than be a king and if you are not upto my standard I will stop teaching. Remember half knowledge is more destructive than no knowledge. So make your decision carefully.
Karna (seriously) : Gurudev, whatever you teach me I will try my best to learn. If I can't it will be my failure. For me A teacher a day if father for life. I will give my complete devotion to you.
Shukracharya (smiles) : Good Putra, very good. You have passed the test. I will teach you as for how much it depends on how fast you learn. I will teach you for three years.
Karna : Thank you Gurudev.
Karna went ahead and touched his feet. Shukracharya blessed him.
Shukracharya : Devraj, please come to me after three years. Till then I will teach Karna as much as he could learn.
Indradev : Yes shukracharya, my work here is done allow me to leave. Putra Karna all Dev's are also impressed by you once you will come to swarglok you will get their thanks and regards. Stay blessed we will meet after three years.
Indradev left and shukracharya took Karna to his hermitage to begin his education. He began teaching karna about various duties and responsibilities of King.