He doesn't need it?
There are a million other ways he could've handled this without murdering people and betraying the ones who took him in, cared for him and loved him. On top of that, we do not have any evidence that the king killed his brother other than Soo-Woon's beliefs.
And I could of course not remember this, but how has the whole kingdom been saved? There's wars everywhere now and thousands are being slaughtered while Soo-Woon wish to claim it all, while the former king was merely pacifistic and didn't wish for war.
The way the author has to communicate with the audience is by making a character say something and others character to re affirming it, until this point on the story there hasn't been any character who denied what Soo won stated therefore we have to believe it's true (since the author is really the one saying king ll killed Soo won's father), now that we can assume that the former king murdered his brother, then is understandable that the son wants revenge, "eye for an eye and a tooth for a tooth, he's just killed the man who took away his father from him, and on the time the story is set it's "alright to kill", there's war everywhere, millions of people have kill or are were killed, in other words is the survival of the fittest, even our main cast has done it, the dragons, hak, Yun (to survive on the fire tribe) and even yona, so if you're using this argument to defend Yona and condem Soo won, aren't you being a bit hypocritical?
Before Soo won stepped in, the kingdom was seriously weak, people were dying everywhere, countries were being taken away, and the fire tribe joined another country to betray the king. It's true that Soo won fought a lot of war, but those were necessary wars to gain strength and power since other countries perceived the kouka as an easy target and it was a matter of time for them to attack. The former king wouldn't have been able to survive even the betrayal of the fire tribe
Just have to say one thing. Everyone is saying Soo Won has been fixing things, but honestly he really hasn't. Most of the time it's been Yona, Hak, and the dragons stepping in. They have found food that can be grown in places where fields were empty. They have been defending the people on the boarders, and often have taken care of things before Soo Won has even gotten there. Soo Won hasn't seen the battle field nearly as much as Yona, and with out her, hak and the dragons, he would have lost many more people or failed all together. So while Soo Won did unite the tribes, what would happen to that unity if it were known that he not only killed king iL, but also tried to kill Yona. Especially now she is seen as the one to bring the dragons home. If Yona wanted to tear the kingdom apart she could just by taking the dragons and leaving, and revealing all that Soo Won has done. Yes the wars were necessary for the kingdom, but it wasn't Soo Won fighting them.
I hate to desagree with you but those but even though Yona helped a lot, the problem could've been solved one way or another. Yes, Yona provided a handful of the plant that could grow on the fire tribe, but Soo won talked to the head tribe, educate him to be a better leader, end money and doctors for people with decease, and gave them a whole lands of those plants plus the citizens of said land to teach them how to how the plants and cared for it.
They got first to the water tribe, and they wanted to do something against the drug but couldn't because that would become an international issue with the other country, it was Soo won convince Lily to move the soldiers, and made the strategy to defeat the drug dealer and company, later on he used his power of king to save the slaves and to ensure that drugs aren't exported to kouka anymore.
What am trying to say here is that even though Yona is helping, there's a limit of what she can do to help, she can change the life alot of people with her actions, but Soo can help a whole tribe with his actions, and that's not surprising, after all he hold the highest power on the kingdom so he can do a lot more.
By the way don't forget that every time we see Soo won involved in something, he got there after yona, that means that even if she wasn't there, he came to fix the issue, so it would have been fixed regardless of whether she was there or not
Actually as far as the fire tribe goes it was Yona that helped with their medical teaching because of Yoon. She was the one that got the youngest brother to start planting the seeds and to help care for the people of the outer villages. Soo Won didn't know about the seed until after Yona brought it back and the youngest prince of the fire tribe informed him of it. Yes Soo Won helped the elder brother, but he was not the one that saved the fire tribe from being eliminated because the father and current leader the fire tribe betrayed kouga kingdom.
As for the drug trade Yona got the ball rolling on that and both Soo Won and Hak worked together to free the slaves.
The times that Soo won showed up after Yona and her friends left if they had not been there Soo won would have been to late. Like when they saved the girls from the slave ships, if Yona had not been there Soo Won would have not made it in time to save the town. So I stand by what I said, Soo Won has brought the tribes together, and while he is helping the leaders take care of their tribes better, Yona is the one that is defending the people that Soo Won cannot reach. They are the ones moving with the freedom that Soo Won does not have, and thus with out them Soo Won would not be as successful as he has been. I believe that Soo Won more than anyone has come to realize this and that is why he is trying to get along with the dragons. He's not asking for forgiveness, he is just trying to make the best out of a bad situation for the good of the kingdom, just like Yona.
This situation sucks, but neither Soo Won or Yona can do any good with out the other.
Just a reminder about Soo-Woon's two-facedness. I really can't trust a guy who has already shown us that he can't be trusted, no matter how sweet and innocent he might seem. He would've killed Yona, as well, had he had the chance and sent people after her to do so.
Same day:
http://www.mangago.zone/read-manga/akatsuki_no_yona/an/akatsuki-no-yona-chapter-1.html/54/
http://www.mangago.zone/read-manga/akatsuki_no_yona/an/akatsuki-no-yona-chapter-1.html/64/
http://www.mangago.zone/read-manga/akatsuki_no_yona/an/akatsuki-no-yona-chapter-2.html/19/
I can't wrap my head around how people can like Soo-Woon and think he deserves redemption after all we've been through with Yona and Hak due to his actions.