Kazuki seeks forgiveness. Kazuki/Juubei.
If he were to speak, Kazuki does not doubt that Juubei would come to him. Juubei is loyal, devoted, in love (now, always--and Kazuki can do nothing but believe, because Juubei's heart had been promised to him long ago).
Kazuki might say:
"I have missed all that we once shared."
"I need you."
He will not speak of such matters. Juubei's anger had cooled more quickly than it should; Kazuki knows that he does not deserve the happiness he would find loving his friend. Full of noble intent, but cruel without thought, Kazuki dares not trust himself with Juubei's heart so quickly, so easily.
Juubei is his dearest friend, and fierce protector--and Kazuki thinks that he has done little to earn any of it.
There are many things that Kazuki might say.
He says: "I am sorry, Juubei."