Dario Bossi was one of Count Dracula's potential successors, since he was born on the same day that Dracula was sealed away for good in 1999. His most feared ability was his propensity to manipulate fire; this power was conceived in 2035 when a small portion of Dracula's power leaked out from the eclipse-held seal and somehow found itself tenant to Dario's desire. Dario used his new ability for anything but purposes of practicality. In fact, his actions were that of wicked criminal, and in time he became a most-wanted arson suspect in countries worldwide.

His fiery personality and impulsive tendencies pushed him to immediate action, and Celia Fortner's new cult was the perfect platform from which to showcase his abilities and prove himself to be a true Dark Lord candidate. In his first meeting with Soma Cruz, in the Wizardry Lab of the cult's hideout, Dario was unimpressed and ready to tear the boy apart. Dario's allies, Celia and Dmitrii, knew better and prevented their hotheaded companion from spoiling the entire plot with his rash judgment. Patience was the key to achieving their goal, and the flustered Dario would have to wait.

Dario would soon get his first taste of Soma's power in the castle's garden, where the two would see combat. Soma had recently defeated Dmitrii Binov and apologized to Dario for killing his "friend." But Dario didn't care--he was more disappointed that he, himself, didn't get to finish off the posh Dmitrii. It was one less mountain to climb in his lust for Dracula's power, which we wanted only out of pure arrogance.

Much to his own dismay, Dario was rendered immobile by the capable Soma. Even then, Dario still wanted a go. It was Celia Fortner who arrived and talked Dario out of making another mistake. Dario was her last Dark Lord candidate, after all, and the investment was too great. While Dario gathered himself, Celia lay down a challenge for Soma to reach the castle heights.

While Soma scurried about the hideout, Dario made his way to the castle's highest point, the pinnacle, where he would wait, this time, patiently. Soma eventually reached the pinnacle, where the anxious Dario was ready for a rematch. "What's the point of having power if you don't use it?" Dario wondered; it was "survival of the fittest," he believed. Soma was determined to prove that Dario was no "Dark Lord."

While the argument continued, Soma gazed into the chamber's mirror only to notice that Dario's reflection was shrouded by a fiery apparition; upon using a special soul power that allowed him to enter into the mirror world, Soma learned the truth--that a flame demon called Aguni had fused with Dario's soul. Soma cut down the vicious demon and then returned to the physical world, where he found Dario hunched in pain. By destroying the demon, Soma had cut off Dario's power, his ability to manipulate fire. The now-terrified Dario reacted to this turn in the only way natural--he ran away as fast as he could.