1. The guy from the other kingdom, Orikakan, was planted a very heavy suggestion by Niwe of Shikeripitchum. He allowed him to think that Hakuoro was the one who killed his sister and his nephews/nieces in the process. This anger was so great that he went to war with Hakuoro for it and dragged his bodyguard Touka as well. Too bad it was all a lie. As for the real killer, we'll never know.
2. There's no explanation for Mutsumi's unique power. We're left to believe that she's just a very unique experiment from all the rest. Same Mutsumi now as it was before; you might say her consciousness was sealed in Kamyu. Because Kamyu is different (black wings indicator), she can allow Mutsumi to take form and vice versa.
3. Suonkasu was really really in love with Karura. I forget if Karura was a slave to him already or not. Regardless, Karura removed his genitals at one point and fled. She was presumably captured and sent back to Na Tunk when a storm destroyed the ship. Current events take place afterwards.
4. Next to nothing is known about Touka's background. All we know is her species' name and what they're like (Kuuya and Hakuoro trade stories about their Evinkuruga bodyguards). Touka was given a lesson by Karura to best...please Hakuoro...I think. She kinda forced sex on him as a result. = o
5. Yep, Yuzuha got pregnant from their intercourse. Did she die at childbirth? There's no way to tell, but we do know that she died fairly soon after delivering the baby as Oboro was holding it on that cliffside and the child wasn't like 5 years old or something. Oboro knew. He wanted Hakuoro to do it. Well, you may think it's stupid but there was very little time. Plus, Hakuoro didn't sign a contract with Yuzuha/Oboro. He wouldn't be obliged to use his superpowers to save her as a result.
6. Black wings represent her link and capability to have Mutsumi summoned. Kamyu is a special child. Mutsumi has red eyes. Notice that? As for the vampirism, theorists suggest that it was Mutsumi trying to ressurect herself, but that's really difficult (for me) to believe. Black wings were explained somewhat. Kamyu didn't like being different having black wings but that's about it.
7. Nope! Consider it as the human's experiments between Iceman's DNA and various other animals to create a human augment capable of living on the surface.
8. You'd think so. I think so too. But hey, that was Hakuoro's decision in the end. We don't ever know where he goes.
9. This is difficult to answer. After several generations, the DNA gets so broken up that it's hardly called incest at all. But since we don't know how many years went by between Iceman's sealment into the earth and when he woke up as Hakuoro, we don't know for certain. But for me, since there's no proof, and there are other factors included, you can't say for certain they're related at all.