In the future, Byakuran sealed Uni's soul to collect the Arcobaleno Pacifiers and awaken the Trinisette. Upon Tsuna's intervention and Uni coming back to her senses, Byakuran expressed nothing but the fact that Uni was his last piece upon awakening the Trinisette, and anger when 'his toy' died. However in the present during the events of the Rainbow arc, their relationship improved greatly. He became Uni's team boss representative. When Tsuna questioned him about his motive, Byakuran said that similar to Tsuna in the future, he felt the same regarding Uni - he wanted to do things properly and give it his best for the sake of that child.
In the future, Byakuran doesn't really care about his comrades. No remorse was given when they had died despite being their saviour who had helped each of them when they were at their lowest in life. To Byakuran, he hadn't done it out of care, but out of the fact that they had been useful to him and his plans. In the present, his relationship with the Six Funeral Wreaths has improved as it appears that he cares for each of the members compared to his future counterpart.
Byakuran was Tsuna's enemy in the Future Arc and taunted him about his misfortune, while also expressing satisfaction that he had finally found a worthy opponent. Tsuna's older self concocted an elaborate scheme to defeat Byakuran, which succeeded when Tsuna killed him. At present, however, their relationship has improved to the extent that Byakuran defended Tsuna from an attack launched by Colonnello. In his first appearance after returning from the alternate future, Byakuran briefly visited the Sawada residence and was eager to see Tsuna's room. According to Uni, Byakuran and Tsuna are similar in a way neither of them understands.
Byakuran had met Shoichi when they had still been in university and had befriended each other along the way. It was also because of their friendship that they decided to create the game called choice, which is later used as a battleground between the Millefiore and Vongola, to pass the time. In the future, when Shoichi had turned out to be on the Vongola's side, Byakuran had revealed that he had known all along about Shoichi's true intentions to defeat him. Shoichi had been saddened at Byakuran's defeat and death, but he had held strong on his belief that Tsuna had to defeat Byakuran for the greater good. After Tsuna had killed Byakuran and everyone returning to the present, Shoichi seems to have renewed his friendship with Byakuran.