Before the storyline of game
Prior to the game, Vashyron was a soldier assigned to an expedition set by Cardinal Antourion ( a major ruling figure in Basel). However, the expedition goes awry and many of its soldiers were killed. Vashyron was actually meant to be among the dead, only to survive a supposedly fatal blow from an angel-like child. Not long after, he resigned from the military and began life as a hunter (an ex-military person doing varying jobs for anybody rich or poor).
As a hunter, Vashyron was assigned to kill someone who was on a killing spree. He followed the killer to his hideout in a seminary, and subdues him in a fight. Killing the target was another matter entirely; even gun shots to the head proved ineffectual. Realising that the murderer should not be left to his own devices, Vashyron decided to take him into his care. 'Him' turned out to be Zephyr, a playable character who would later aid Vashyron in his work as a hunter. Although the two characters grew close, they never openly discuss the day they met.
During the Game
By the time the game prologue starts, Vashyron is a 26 year old hunter who lives with two other characters: Zephyr (the boy who Vashyron took in, see above) and Leanne, a 21 year old girl who Zephyr saved a year ago. Both work for Vashyron in doing his errands and also are capable of using firearms and weapons. It is quite possible that Vashyron taught Leanne about such skills, although he might have tutored Zephyr as well.
The game starts off with the threesome doing certain odd jobs in order to receive income, such as delivering items or fighting off gangsters. However, as time goes on, the main characters began to learn about the each other's murky origins. Vashyron knew about Zephyr and what he did, but he also learned that Leanne was a guinea pig for an experiment concerning life span manipulation; as a test subject, she was programmed to die upon her 20th birthday, but didn't for then-unknown reasons. Leanne would also learn of Zephyr's misdeeds while accompanying Vashyron to the Crank Seminary (where Vashyron and Zephyr first fought and met).
Soon after her 22nd birthday, Leanne began searching for Juris, a scientist who she befriended as a test subject in the aforementioned project. Vashyron and Zephyr followed her to Aetersyl to rescue him. Upon being rescued, Juris tells Zephyr and Vashyron about how people could be killed by having their quartz (in essence a life stone) destroyed, and how Leanne's quartz is in the posession of another scientist, Sullivan. Vashyron suggested that everyone should forget about the ordeal and move on with their lives, but Zephyr angrily elected to find Sullivan.
When the gang finally tracked down Sullivan, they attempt to take Leanne's quartz for themselves. But Sullivan doesn't have it, and he told the group that it will be destroyed if he is killed. Before anyone could react, Cardinal Rowen kills Sullivan from a distance, wanting to see if Leanne will also die once her quartz is supposedly destroyed. She doesn't, but Zephyr wanted to kill Rowen for attempting to play with Leanne's life in that manner. The threesome then went into the Basilica and killed Cardinals Garigliano and Anturion, setting the stage for the final battle with Rowen himself. However, when Zephyr fatally shoots Rowen the latter doesn't die; Zenith, the machine that controls the life-span of humans, allowed Rowen to live longer. Disappointed with the battle's outcome, the three leave the Basilica.
Vashyyron is last seen to be outside of Basel with Zephyr and Leanne, where the land is unscarred from pollution and where the air is clean.
On the surface Vashyron talks and acts like a mercenary, caring about nothing else but his business and money. However, he shows care for both Zephyr and Leanne, being the main coordinator of the groups's activities and jobs. As the oldest member of the trio, he is the closest thing it has to being a parental figure, especially towards Zephyr.
That said, Vashyron also has a perverted side that he shows from time to time. A swift punch or kick from Leanne usually results when she spots Vashyron attempting to ogle at breasts or female genitalia.
"If you're serious about letting loose those bunker busters, don't be surprised when I return fire with my trusty magnum."
- Vashyron (in his mind), after gazing at the large, bouncy and soft breasts of Cardinal Barbarella
"Daddy does not approve!"
- Vashyron, in response to seeing Zephyr and Leanne in wedding clothing, supposedly marrying each other (when in fact the two are acting as fake newly-weds for a cardinal)
"If you can hold your own, I could use you. Everyone else is just dead weight"
-Vashyron, echoing the lines of his late friend Victor (who died in the expedition, see above)
"That all you got?"
"I can see right through you"
"I can read your every move"
"They [enemies] bit off more than they can chew".