Lambo and I-Pin have a sibling relationship. Lambo is often seen stealing sweets from I-pin, which he will later claim are his sweets to begin with. While his 5 year old self never says or does anything nice to I-Pin, his future self refers to her as "Charming." I-Pin has shown to care for Lambo's well-being either her 5 year old self or her future self. They always stick by each other's side.
Lambo always drives Tsuna crazy, always bothering and annoying him to no end, constantly asking him to play whenever he feels bored and show no respect to him, calling him "No Good-Tsuna." However, his future self said that he never regarded him as his boss but more like an older brother, thinks of him as a great brother. Tsuna also worries over Lambo's well-being and reluctant to drag him into battle, always trying to avoid him from it and will save him if he's in trouble.
Lambo is really attached to Nana who he refers as "Mama" and is constantly being spoiled by her. Nana is also the reason for his ability to emit flames when he fought Kikyo's Box Weapon. Nana treats Lambo kindly like he's her own son and is always patient with his behavior.
Both have somewhat brotherly relationship; Lambo and Gokudera bicker constantly and call each other names (Gokudera refers to Lambo as "Stupid Cow" while Lambo refers to Gokudera as "Stupidera"). The two share little respect for each other but at times Gokudera can be very protective of Lambo.
Lambo shares a mutual disliking with Lampow, due to the latter seeing him as an immature, petulant child. It causes the two to always get angry or annoyed whenever they meet. Lampow has stated that he hates kids, especially kids like Lambo whom he calls a "snot-nosed brat" and refused to deem him worthy before he even tested Lambo. Lampow nevertheless deemed the boy worthy of his inheritance when Lambo used stored-up electric energy in his horns to protect the rest. Ironically, Lambo and Lampow are almost the same in personalities: annoying and unwilling to fight his own battles.
Kyoko, Haru, and Lambo are close and are usually always together. Haru hates whenever anyone hits or harms Lambo, such as Gokudera who is always picking on him. However, one time Haru choked Lambo by hugging him too tightly. In the future Lambo is always seen with Haru, Kyoko, or I-Pin. Whenever he is bored he goes to Haru, Kyoko, or I-Pin to play with them.
Lambo took a quick liking to Large, which Large returns, and ever since then they get along pretty well and always play together. Large's very patient with Lambo's attitude and doesn't seem to mind when Lambo claimed him as his subordinate. However, Large showed no hesitation to kill Lambo at the battle in Simon Island as his Family is much more important than Lambo. However, they later reconciled after all the misunderstandings between the two Families cleared up and often play together again.