...other then with Tsuna, Colo or Vongola Nono

Bianchi is a constant presece in Reborn life if we can say so. She was Reborn's partner even before Reborn took the curse upon self, and seems that she really loves him. Reborn trusts her with jobs and everything, but I'm actualy not sure he feels the same emotion as she does.
Bianchi also known as Poison Scorpion Bianchi is Hayato Gokudera's older half-sister, and she is specialised in poison cooking, to which she is imune.

Dino the 10th boss of the Cavallone family, is Reborn's former tutor, and he can understand Tsuna the best when it comes to the tutoring of the creazy infant. As Tsuna, Dino also didn't want to have anything with the mafia in the begining, but after Reborn tought him, he became half decent boss, who was able to make of the Cavallone family third most powerful in the mafia underground. I said half decent, because he losses all his power if his subordinates aren't around, his main power actualy comes from the love that he has for his famiglia, and when his subordinates are there, he has the main strainght. Reborn also gives him the job to tutor Hibari and prepare him for the Vongola turnament. He is also known as Bucking-Horse Dino. His pet is a turtle named Ezio.

Lambo has a strange relationship with Reborn, on moments it seems like Reborn doesn't even notice him, or at least he doesn't notice the attacks that Lambo as a 5 year old Hitman makes trying to kill him. On the other hand it seems that Reborn actualy believe in him, because he chooses him as the Thunder guardian, he still thinks he is good enough to be part of the Vongola family, and not as a normal member, but actualy as one of the guardians. This small boy, who dresses in a cow suit is actualy really unusefull while small, but his weapon is a 10year bazooka that takes from the past 10 years older Lambo, so we are able to see a 15 years old Lambo and also a 25 years old one, when the bazooka is used twice. He is completly resistant to electricity and that is his main power. From the ring box he recives, he gets a bull.

Yamamoto Takeshi is the one who has been chosen as the Rain Guardian in the Vongola family. He has a peculiar relationship with Reborn, because during the future arc, Reborn actually tells him about the Arcobalenos and why he is an infant, that means that Reborn has a deep trust in this always smiling boy, he trusts him that he won't go telling others about it. And in fact, when they ask him, he simply smiles and says he can't tell. Yamamoto is actualy a simple guy, who's life dream was to become a pro in baseball, but in the end he becomes one of the most trusted members of the Vongola. His weapon of choice is a katana, or better a baseball bat that transformes in to a katana. He is always with a smile on his face, but when the things go serious, he can be really serious.