best friend
From the beginning, it's clear that the two of them are very close. In fact, one of the first things we see Rimudo say to Soruen is that Soruen is the only one he can believe in and nobody else -- not even the Genbu no Miko. Soruen had been like an older brother to Rimudo since his happy childhood, before his sad fate came to light. However, after the death of his father at the hands of those who were hunting the prince down, Soruen came to resent him somewhat and said some harsh words, which upset him. Soon after, Rimudo, still only a child, was hanging from the edge of a cliff. Soruen was holding onto him, but he had the thought: why not let Rimudo fall? Wouldn't all his troubles be over then? Just as he had these thoughts, however, as if the child realized what Soruen was thinking -- Rimudo smiled brightly. Go ahead. Let me go. he seemed to be saying. At that moment, Soruen realized how selfish and awful he was being and pulled the young child up, hugging him. They would be inseparable from then on. Rimudo became bent on getting revenge by killing his real father, Temudan, and while Soruen knew that this wouldn't help the prince in the long run (not emotionally or otherwise), he went along with it, secretly hoping that the priestess of Genbu would someday come and set Rimudo free. Of course, that was just what happened and Takiko suddenly appeared in their lives one day.
Soruen could sense that Takiko and Takiko alone could understand Rimudo best and save him from his miserable fate. He opened up to Takiko and though he hadn't known her long, was eager to tell her the truth about Rimudo's past.
I would ask you to please call forth Genbu. Rimudo-sama hates the seven celestial warriors... But he is a star destined to save this country! When he's together with the priestess, the way of life he originally had will...
Soruen had a lot of loyalty to Rimudo, but he also wanted Rimudo to be happy, so this meant that sometimes he had to act against what his prince would have wanted because he knew better than Rimudo did. This was proven when he and Takiko were captured by Kutou. He gave Takiko the toku seed with the distinct smell that was how he and Rimudo had always been able to find one another. So, when he and Takiko were separated, Soruen went to his death and Rimudo pursued Takiko instead -- thinking that the scent of the toku seed would lead him to Soruen. By the time Rimudo realized what had happened, he was too late and Soruen had passed away in order to protect the priestess -- in order for Rimudo to be happy.
Even though Soruen died, his presence is still felt in the series. Rimudo suffers a heroic BSOD for a time after this and only comes to after Takiko arranges for an elaborate send-off ceremony. Even after that, however, visions of Soruen come and go -- when Rimudo is heading towards Touran to find Takiko and collapses in the midst of a snow storm, for example, it's the memory of Soruen that gets him on his feet again. Thus the friendship between Soruen and Rimudo is really one that manages to best even death.
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