Basil is the first person in the series, other than Tsuna, to go into Hyper Dying Will Mode. Iemitsu, his master, gave him the Dying Will Pills that Basil uses to go into Dying Will Mode, which were later given to Tsuna as a gift after the Varia Arc, before going back to Italy with Lancia. His Blade and Tsuna's X-Gloves may have originated from the same material, seeing as Basil is able to utilize his Rain Flame to light it. He made a big difference when helping Tsuna train before Tsuna's fight with Xanxus. Toward the end it would seem that Basil and Tsuna created a strong bond between them.
Basil is the first person seen in battle during this Varia Arc (along with Squalo) and he is seen with a picture of Tsuna's immediate family. He accidentally leads Squalo to Tsuna and his Family while they are out, mistakenly believing Squalo to know who his target was. After being tossed aside by Squalo, he watches as Yamamoto, Gokudera, and Tsuna all take him on, only to have to step in to save Tsuna from being severely wounded. Basil tells Tsuna of the Half Vongola Rings he is carrying, and then he is forced to do battle with Squalo once more. He, in the end, is unable to fend Squalo off, and is knocked unconscious, after which he recuperates in a hospital for a while.
Throughout the first six Ring Battles, Basil helps Reborn to train Tsuna, even after he lost the Sky Vongola Ring in the Lightning Ring Battle. The training paid off when Tsuna was forced to take on Gola Moska, and again when he had to fight Xanxus. When it is revealed that the Varia had planned to kill everyone at the Sky Ring Battle and take all of the Vongola Rings, Basil volunteers to help Tsuna's Family to fight, but he, Shamal, Dino, Ken Joshima, Chikusa Kakimoto, Colonnello, and Reborn are all trapped due to the Varia's cheating. Basil is very eager to help Tsuna.
When Basil came to the future, he arrived in Spain, where he found a Box Weapon and the Helper's Book, which had recorded the Future fighting style. He then made his way to the Vongola Base in Japan while fighting the Millefiore on the way. Not long after Basil's arrival, Tsuna's Vongola Box went berserk, but with Yamamoto's help, Basil was able to calm it using the Rain's Tranquility. Dino later instructed him to continue with his training, while helping the others at the same time.
Later, after the Vongola lost Choice, Basil along with Ryohei and Gokudera was injured while trying to protect Uni from the Six Funeral Wreaths. The next day, he was grouped with Lambo and the injured.
Ryohei, Tazaru and Nosaru in order to defend Uni. They first encountered Kikyo, but soon it bacame a full-out war between the Vongola and the remaining Six Funeral Wreaths. During the fight, the final Funeral Wreath, Ghost, appeared. Basil, Ryohei, and Gokudera attempted to combine their attack power but it had no effect.
After Byakuran was defeated and everyone returned to the past, Future Basil was seen with the Vongola Guardians waiting for Future Tsuna.
In the CEDEF headquarters, Basil was seen along with Oregano informing Iemitsu that they had an Arcobaleno customer; this is later revealed to be Colonnello. Later, after Oregano confirms with Lal Mirch that she was going to fight for Colonnello, Basil pipes in that he wanted to go to Japan as well, as he wanted to fight against Tsuna. Later, when Basil arrives in Japan, he happily states, after Nana agreed to allow the CEDEF to stay at their house, that he was excited to be able to train with Tsuna, as he was eager to fight against Tsuna's more powerful self. Basil also expresses his surprise along with everyone else when Byakuran arrives and proposes to Tsuna that they form an alliance.
2nd Day of Representative Battle of the Rainbow
Five minutes ago before the end of the day's battle, Basil had gone to spy on Team Skull on a nearby lamppost, and finds that no one had challenged them, and that they were just going on with their normal bickering lives. However, a flare suddenly explodes and everything is silent. Basil is curious and sidles up to a window and looks through: he sees a large group of Vindice, led by Bermuda and a Vindice with Jaeger appear; all members of Team Skull except for Skull are mortally attacked and injured, pierced with chained weapons. Skull, on the ground with a spilled half-eaten bowl of rice, trembles in fear as he sees the perpetrators. Skull wonders who they are, and the baby Vindice identifies Skull as the Cloud Arcobaleno. Skull sees that the baby Vindice has a transparent pacifier, and the baby Vindice states that he had taken a great interest in the Representative Battle of the Rainbow. Basil is hiding behind a wall and watches the Vindice and Skull's conversation, and wonders who the bandaged baby was. Basil is shocked, when Jaeger revealed turns around abruptly and sees him.
He immediately called for ambulance for Team Skull to be taken to hospital, and later met Tsuna, Yamamoto, and Gokudera there. Basil explains that even though they're heavily injured, fortunately, the injuries are not dangerous and they'll be fine soon. He apologizes that he's unable to assist Enma and the others as he was paralyzed in fear upon seeing the Vindice.
Shortly after back from hospital, a Vindice ambushed Sawada residence while Collonnelo went to Arcobaleno meeting at the hospital in Skull's room. He, Lal, and Iemitsu fought him and able to cornered him. However, the Vindice then attacked the house, which caused Nana to come out after hearing the commotion. This gives the Vindice opportunity to attack her and made Iemitsu protect her at the cost of his boss watch destroyed, disqualifying Team Colonnello from the battle.
4th Day of Representative Battle of the Rainbow
He, along with Enma and Tsuna are chosen to become Commando Unit who will defeat the Vindice one by one while Jaeger and Bermuda are occupied by Mukuro, Dino, Xanxus, Squalo, and Byakuran. They first ambushed Alejandro who was supposed to defeat Team Mammon that turns out to be a decoy puppets. With their teamwork, they able to defeat Alejandro and his Ginger Bread dolls. They immediately went to the parking lot where Small Gia and Big Pino are. They able arrive in time right before Gokudera, Yamamoto, Chrome, and Fran are hit by Big Pino's cannon. Small Gia switches his weapon as he attacks them. Enma and Tsuna able to defend themselves with their flames. However, Small Gia able to break through Tsuna's barrier and drag Basil out from it as Big Pino shot his cannon, hitting Basil and destroyed his wrist watch.