Seiryuu Seishi Suboshi
Real Name: Shunkaku Bu
Suboshi first showed up when Nakago revealed his plans to Yui. He said that he had planted a spy on the Suzaku camp and introduced Suboshi as its twin. The two had a connection and communicate with their wrists, as shown in the series. When his brother "died", (he said that he couldn't sense his aniki's chi anymore) he felt that his world had fallen apart. He spent his entire life crying alone in a dark room, saying that no one can help him. That was until Yui approached him and tried to comfort the poor Suboshi. Suboshi once again felt that he was loved and cared for, so he decided to protect Yui with all his life so that he would not lose another loved one again. But then, he couldn't forgive Tamahome for "killing" his brother, as he believes. Convinced by Nakago, he went toe the house of Tamahome and killed all of Tamahome's family, so that Tamahome can feel what he has felt on the loss of his aniki. Tamahome DID feel it, and approached to kill Suboshi, but he was saved by Soi.
Since then, Suboshi was always shown with Yui, protecting her everywhere she goes as his errand boy. He doesn't care if Yui has no feelings for her, as long as he can protect her and always be with her. When Yui told Suboshi that she was raped and tells him that it was Tamahome's fault, his anger for Tamahome rose. 
After that, he came back to his beloved Yui. In the summoning ceremony, he hugged the confused Yui and told her that he will always be there for her, that's when Yui came back to the real world. Suboshi participated in the war against Konan until Nakago ordered him to go to Yui's world (instead of Nakago) to comfort the Lady Yui. Yui was not as happy when Suboshi came instead of Nakago. She was always asking herself when would Nakago come to help him. Suboshi caused so much trouble in the real world, especially the moment he had found Miaka and Tamahome. He ran around the whole town chasing Miaka to kill her, but then Tamahome came. After a long, boring speech by Tamahome saying to Miaka that he was born to protect her, the fight started. Suboshi had almost got Tamahome and said that he won't be fooled f Tama's trick (going on his back so that his ryuuseisui would go through him) and was about to kill Tamahome when he was stopped by Tamahome's siblings. It therefore caused his death, but before he died, he held Yui's school ribbon and cried her name, and his brother's. (but just barely..like A--mibo---sh...then died)That's when Amiboshi cried and told his "parents" that "like some part of his body was ripped apart from him, no, it's like a missing part of me has filled me in" or something like that. 
My Take: The twins were really different, even though they look alike. The war had brought them different perspectives in life. For Suboshi, being very dependent, loved those who cared for him to a point that he would do anything so that he could not lose them. It was all because in the war, he experienced sadness that his parents, whom he loved so much died. He doesn't want to experience anything like that again so he became very protective and attached to his "aniki". He doesn't even want to see his loved ones hurt. That's why I understand why he killed Tamahome's family, as innocent as they were, being motivated by Nakago and all. I really didn't feel sorry for them because Suboshi had experienced more. (hey, it's my opinion!!!) I like his devotion and protectiveness to his loved ones, and I especially admire him when he made Amiboshi forget and took him to the village. For me, it was really the greatest sacrifice in his life. He loved his brother so much that he sacrificed his happiness for his brother to gain the happiness he longed for, and that's really sweet. Thinking about it, it's a very hard sacrifice and I couldn't even think of doing it. He's really not a bad guy as Tamahome percieved. His only fault is that he loves so much.