When Kurama had received the spirit of words, he suspected that ultimately the purpose would be revenge. After betraying the young demon as he had, it could hardly be called unexpected, though the timing itself was curious.
When he met him after a thousand years, and was tested immediately by middle class demons, he knew something had been learned when he abandoned him centuries before, but wasn't certain what.
And then when Yomi revealed the bug he had hired years and years before, he himself betrayed his true feelings of regret, losing control of his heartbeat. Yomi believed it to be guilt. He was partially correct.
When he watched Yomi battle his own son he saw a slight reflection of what he himself had tried with him for years. And he was proud then. He had taught Yomi to fight, how to improve his techniques -although the teachings hadn't been applied when he was around. But he was, in the depths of his heart, glad. Glad that he could have had something to do with Yomi learning that level of patience, dispite what it may hold for him in the future.
Then came the most shocking thing yet, although part of Kurama, the part he had forgotten he had before Youko became infamous, laughed at himself and knew he should have known. Yomi had rescued him - had gotten to him far before even Hiei had arrived. And there had been a tentativeness that he had not sensed in him since long before he had 'become a liability', one that he would have expected in a child like Shura, wondering if his actions were approved by his guardian.
And Kurama, torn, and believing that he shouldn't be given this chance, backed off. Or thought he did. Away from the chance to repair what had been shattered.
"Have you forever deserted yourself as Youko?"
"oh no. I never leave anything behind. I never have."
Then, after Yusuke and Yomi's fight, when he had left for his 'journey of truths' with his son. Yomi had all but flat out said "I forgive you." And the actions of his son... Although he wasn't certain that Shura was aware of the entire story, the child was enthusiastic, even eager to get to know Kurama, the man his father respected.
Kurama was astounded. He had never expected to be forgiven by the man who he had known as a hot headed, foolish youngling, and treated as such.
But mostly, he was proud. Yomi had grown to be more of a man than he was.