Lancia was an orphan that was adopted into a Mafia Family. Because of this, the Boss and Family that brought him up were his life. So, in order to repay their kindness, he served the Family as a bodyguard until he became known as the Strongest Man in Northern Italy. Five years before the events of the Kokuyo Arc, the Boss picked up another orphan and he became his responsibility. He loved him like he was truly part of his Famiglia like the way his Famiglia treated him. After coming home from playing cards one day, he found that everyone in his Famiglia had been killed. In reality, Mukuro had used the Possession Bullet to take over Lancia's body and use him to commit that murder. Because of this, he kept having nightmares of the incident and eventually tried to commit suicide; however, he couldn't, because he was under Mukuro's control. Eventually, he lost his name and will and became the fake Mukuro Rokudo. Lancia did everything and anything for him and became a killing machine.
Lancia is first seen in a photograph after Ken Joshima is defeated that falsely identifies him as Mukuro. He is in the room when Chikusa Kakimoto regains consciousness and is described as one the reinforcements that was called in to help deal with the Vongola. He leaves and confronts Takeshi Yamamoto, Hayato Gokudera, Bianchi, and Reborn. Because of the photo they all believe him to be Mukuro.
Yamamoto is the first one that tries to fight him. After attacking Yamamoto with his Steel Serpent Ball Yamamoto finds out the weapon's ability to redirect air currents by throwing dirt into the path of the ball. He defeats Yamamoto and then Gokudera collapses because of the side effects of the Trident Mosquitoes, and Bianchi prepares to fight him. But before he can Tsuna arrives asking what's happening and blocks his attack on Bianchi.
Tsuna evades his first attack and punches him in the jaw. He then blocks and throws his next attack back at him. But that is still not enough to beat Lancia. He tosses his Steel Serpent Ball into the air and engages Tsuna in hand-to-hand fighting to put him into position so the ball in the air would land on him. This doesn't defeat Tsuna because he declares that Lancia isn't an evil person and because of that his weak will won't beat his dying will. In the final attack he defeats Lancia because the guilt in his heart prevented him from giving the finishing blow. He then admits that he isn't the real Mukuro, and that Mukuro took everything from him.
He tells Tsuna about his Famiglia and how they were all killed by his own hands because he was being controlled by Mukuro. He then tries to tell Tsuna about Mukuro's true objective, but he was attacked and poisoned by Chikusa to keep him quiet. Before he passes out Tsuna asks for his real name and when Tsuna repeats his name it brings him peace as he becomes unconscious.
While Tsuna is fighting Mukuro and is hit by rebuke bullet he hears Lancia telling him not to make the same mistake he did by protecting his friends and family with his own hands. At the end of the arc, he was treated for the poison and then taken away by the Vindice.
When the Varia called in reinforcements after the failure of the rings accepting Xanxus as having Vongola blood, they all appear defeated. Lancia then finishes off the rest off them revealing that he defeated them. Because he isn't being controlled he is stronger because now he is without doubts. Although he has no more ties to Mukuro's gang, Mukuro asked for Lancia's help in fighting for Tsuna. After the battle, he stays at Tsuna's place for a while. While trying to leave without bothering anyone Lancia and Basil are confronted by Tsuna who question why they left. He speaks about how he thinks that he can sense Mukuro better than other people because of all the years he spent being possessed by him. He plans to return to Italy with Basil to begin visiting the Families of the people he killed to make amends. Before leaving, he gives Tsuna his former boss's ring. The Ring has a stone in it that looks as if it could emit Sky Flames, as its core is orange.
During the Future Final Battle Arc, Lancia's boss's ring protects Tsuna from Byakuran's needle attack aimed for the former's heart.