V one day shows up at Dante's shop to hire him for a job, one that involves stopping a powerful demon, different from any other he's faced before. He phrases it as being his "reason for fighting". In truth, this reason is his brother Vergil, the true identity of this powerful demon that has taken root in the city of Red Grave where the twin brothers grew up.
V was born from Vergil, when the latter seperated his humanity, and wisdom, from his demon half with his own sword Yamato. When they initially meet Dante asks him his name to which V jokingly replies "I have no name, I am but two days old" both a direct quotation of William Blake's poem Infant Joy, but also an actual cheeky reference to his birth, being he was created on May 1st two days prior. This showcases that V isn't above being jovial, and also reveals some deepers aspects to that of his original self, Vergil. It also presents V's love for poetry, something he isn't shy to hide as he repeatedly recites poetry both when he's powering up his Devil Gauge, but also when he finishes off his enemies.
The process of his birth also what lead to the creation of V's three familiars, Shadow, Nightmare and Griffon, all whom are based on Mundus' minions from the first name--They represent Vergil's trauma during his time as a forced servant of Mundus named Nelo Angelo. A lot of Vergil's pent up feelings toward Dante are stored inside of V, something that is made evident when he finds the unconscious Dante and has a sudden urge to stab him to death only to puncture the ground next to his face with his cane.