It may contain SPOILERS.
Continue reading at your own risk.
Bianchi is the daughter of an unnamed mafia boss and his legal wife. She once dated a man named Romeo, whom she is implied to have killed with Poison Cooking. She then worked, and fell in love, with Reborn.
Bianchi is first introduced with her goal being to kill Tsuna to free Reborn of his responsibility to train him. She attempts to accomplish her goal by feeding Tsuna her special Poison Cooking. Over the course of the Arc, she lightens up on her attempts to kill and settles into a role where she causes comedic conflict. She perfects two new killing techniques in addition to her original one. She mistakes Adult Lambo as Romeo, her ex-boyfriend, and almost kills Adult Lambo with her poison cooking. Bianchi had a terrible relationship with Romeo, and every time Bianchi thinks of him, she becomes upset. Eventually Romeo's ghost tried to get revenge on Bianchi, but ended up being defeated by her Poison Cooking.
Kokuyo Land Invasion
Bianchi takes on her so-far most important role. She accompanies Tsuna, Yamamoto, Gokudera, and Reborn to Kokuyo Land to face off against Mukuro's group, after being worried over what may happen to Gokudera. She has her first and so far only major battle against M.M. after Yamamoto defeated Ken. Using her Poison Cooking to shield her from M.M's Burning Vibrato, Bianchi was able to get close enough to use Garden of Poison Varieties on her Clarinet, rendering it useless and causing M.M. to pass out from ingestion of the poison.
During their stand-off with Birds, she placates him by punching Tsuna, and thus filling his first condition, when Yamamoto and Gokudera refused, and stated that she is used to being hated. However, it is all a show for Birds, as she put hardly any force behind the punch.
Her final role during the Arc is being possessed by Mukuro Rokudo along with Ken, Chikusa, and Hayato. Even after Tsuna gained the X-Gloves and defeated Mukuro-Ken and Mukuro-Chikusa, he tried to use her and Gokudera's body, anticipating that he would not use the same level of force against them. However, Tsuna ends up absorbing their attacks to expend the energy and knocks both unconscious.
In the Future, Bianchi had traveled with Fuuta in order to gather information, but later returns, revealing crucial information about the Millefiore. She trains Hayato to control the rings and boxes, but he later trains on his own. She has a Storm flame, and when she combines her box and ring, she is able to summon scorpions which emanate the Dying Will Flame, called Scorpione De Tempesta (Storm Scorpions).
During the Future Arc, Bianchi takes on the role of tutor to train Gokudera for the Merone Base Invasion. She is the one who gives him the Sistema C.A.I., at first to train with in the "Storm Room" Gokudera's future self-created. She taunts him about his illegitimacy through the initial Storm Room training, only later to reveal that she knew it would bring out the best in him. She tells her brother to try and destroy her Box Weapon Scorpions within the alloted time in a very low visibility setting. After the first session, Hayato does not return.
Bianchi again comes to the foreground as a tutor right before Choice, but this time to Chrome. They train in hand-to-hand combat, with I-Pin to help out. During the girls' strike, she supports Haru and Kyoko's decision to stop doing housework until the boys tell them what's going on. However, she also tells them what the boys are most likely thinking, and convinces them to call the strike off.During Choice, she watches Tsuna, Gokudera, and Yamamoto battle Byakuran's underlings, along with everyone.
After Choice, she goes back to the base and retrieves something, revealed later to be the love letters sent by their father to Gokudera's mother. She is also the one who protects Haru and Kyoko from harm, and comforts them when Uni and Gamma sacrifice themselves.
After the final battle with Byakuran, she says goodbye to Haru and Kyoko, with the promise of giving a letter to Hana from Kyoko. She also finds Gokudera and reveals to him the truth about his mother and their father, using their father's love letters to his mother as proof, but before Gokudera can show his full reaction, they are interrupted by Spanner's Anti-Byakuran Mosca.
Bianchi is first briefly seen watching Reborn worriedly when he was awoke from his dream, and later seen again observing while Nana is angered at Tsuna for badmouthing Iemitsu, his father. Later, she was seen carrying an unconscious Nana who fainted after being hit by Iemitsu's blood while wondering why Nana had to go through such an ordeal. She then request that they make it so that when Nana wakes up, she will think it was a dream.