About their relationship
How they met
Fuuko is running toward Koran Mori's Castle when she bumps into Raiha. He offers to take her to have a look around the mansion. Fuuko's curiosity gets the best of her and she runs off without Raiha and gets caught in a trap. The small area begins to fill with water and she passes out. When she wakes up she finds herself in Raiha's lap with him smiling down at her.
These two are an odd pair. You'd think they'd hate each other being on different sides and all. Fuuko has shown an interest in Raiha, and doesn't mind him being around. Raiha enjoys being with her, he has even said that he wants to be with her. Raiha has become almost like a protector of Fuuko. Similarly to how he saved her life when they met, Raiha again saves her life when she is caught by Sokakusai and she loses her desire to live when he sucks her into his Tamasui no Tsubo Madogu (Soul-sucking pot). Raiha appears to fight Sokakusai. Sokakusai tells Raiha that Fuuko is inside his madogu and Raiha happily jumps right in. After getting Fuuko back to normal, Raiha and Fuuko escape the madogu. Raiha's anger towards Sokakusai brings out his other side. First Raiha says to Fuuko: "Fuuko, please close your eyes. I don't want you to see this". When Fuuko closes her eyes Raiha turns to Sokakusai. Sokakusai begs for his life, but Raiha only looks at him with pure hatred and replies: "What did you say to those who told you those words?" He then mercilessly slaughters Sokakusai.
When the final fight with Koran Mori is coming up, Fuuko had already used up her last Kodama, meaning she can no longer summon Fuujin, making her the weakest member of Hokage. While out with Ganko, she runs into a mysterious man that tells fortunes. When he reads Fuuko's he says that he sees the Shadow of Death in her future. He then gives her a message to meet him later. Fuuko goes to met the mysterious man who turns out to be Raiha. Fuuko slaps him around like she usually does but suddenly Raiha shows his other side and holds his sword to Fuuko's face. For the first time around Fuuko, Raiha shows his serious and dangerous side. He tells her that she will die in the fight with with Koran Mori. Raiha says:
If you insist on fighting Koran Mori, you will die. Miss Fuuko, you're not ready. But if you have the strength to survive a battle to the death, prove it. Show me what you've got. Otherwise, give up.So Fuuko and Raiha fight non-stop for three days and nights without rest. Fuuko manages to get the upper hand in the end and wins. Raiha gives Fuuko the main sphere of Fuujin. He tells her he wanted to be sure that she was strong enough to wield Fuujin's true power and he says that she passed the test. He also tells her about his madogu, Raijin, the evil counterpart of Fuujin.
That's as far as I am right now, sorry, once I get to more parts with these two I'll add more. (I prefer to buy the official manga that is only up to volume 24 right now instead of downloading fan scanlations because the way I see it, the sooner I can read the manga, the sooner it'll be over. And I don't want it to end yet T_T