The Seiryuu seishi are seen as weapons to be used by Nakago, especially in the case of Miboshi and Ashitare, but less obviously concerning the twins. He feels no guilt over using his comrades and causing their deaths by sending them after the Suzaku seishi.
Yui
Since Yui is Seiryuu no Miko she should be Nakago's superior, the one he must protect at any cost. Unfortunately this is not the case. Yui's confusion of mind and jealousy over Miaka allows Nakago to manipulate her for a long time. He believes him over her childhood friend - which should tell a great deal about Nakago's charisma.
Nakago does not seem to care for Yui as a Miko. By being there for her he can ensure that when the time comes Yui will do as he wishes. It is doubtful whether Yui really thought that Nakago cared for her, but at that time of her life she needed to feel loved. By allowing herself to believe Nakago's words she could assure herself that there was at least one person who found her important.
Soi
Soi is Nakago's lover and the one who cares for him the most. She is deeply in love with him and would do anything Nakago asked. She has the power to control chi through sex and uses it to heal Nakago after he has been injured. Nakago seems to respect her more than most, as during one occasion he is the one giving his chi to an injured Soi through the Bouchuu. Soi wants his love more anything and because of that she does things she would not normally approve of. Nakago's treatment of Ashitare horrifies her and she seems to have no ill feelings towards the Suzaku seishi, but she does not protest, fearing that she will loose his approval.
Does Nakago love her? That is not made certain, but he cares for her more he does for anyone else. It is probable that he took her love for granted, never stopping to examine his own emotions. The only time he shows real emotion is when Soi makes a great sacrifice for him. Nothing else could touch him and in the end, his last thoughts are of Soi.
It is my personal belief that Nakago loved Soi, but was afraid of his emotions at the same time. When he had been through so much before he must have felt that by closing off his heart he could be safe from any further injury. If it was known that he cared for her his enemies in Kutou would not have hesitated to use that against him. By denying his feelings he was also keeping her safe.
Tomo
Tomo seems to be the seishi Nakago values the most after Soi. They discuss
strategies and he respects Tomo's powers. Beyond that Nakago has no feelings
for him. Tomo, though, is in love with him. It is probable that he never
revealed this to his Shogun, but Nakago must have noticed it. It was another
way of ensuring Tomo's loyalty. Soi and Tomo have a rivalry because of
this, but when Nakago is not around they are quite capable of working together.
Rivals: the Suzaku seishi
Even though the Suzaku are his greatest enemies Nakago never seems very worried that they might actually succeed in defeating him. He sees them as weaklings, who believe in unreliable things such as friendship and love. Since he is nearly always one step ahead of the Suzaku seishi he cannot respect their intelligence or talents greatly. He sees them as more of an annoyance than anything else, a convenient excuse for launching a war and persuading Yui to support him.
Tamahome
The Suzaku seishi who could be called Nakago's counterpart, as both are favored by their Miko and the most powerful of their respective groups. They are opposites in many ways. Nakago is calm and composed, Tamahome is hotheaded and emotional; Nakago is older and in a high position, Tamahome is inexperienced and a wanderer. They clash many times during the series.
Even though Nakago is more powerful he seems to have an interest in Tamahome, delighting in torturing the Suzaku seishi verbally and physically. Nakago never misses an opportunity to use Tamahome's emotions against him, goading him into a rage. He might well be jealous of Suzaku seishi for having many of the things he was left without: a family, a love and caring friends.