Rosetta was the executive and founding member of the crime syndicate, 'Reservoir Snakes'. But she left the gang to live the life of a wandering huntress.
Rosetta's early life was full of pain from being in a place called 'The Wolf's Belly'. 'The Wolf's Belly' was a facility that kidnapped abandoned children in the slums and raised them to be combatants. It was called hell itself as the children were both tortured and forced into the cruel training practice of pitting each other to death. Despite this, Rosetta waited for a chance to retaliate. When she met Olivia, who shared the same ideals, they decided to leave this hell together. They stole weapons and eliminated all members of 'The Wolf's Belly'. She and Olivia burned the facility down to eliminate all of its traces. Rosetta and Olivia didn't want the hell they've been through to be repeated, so they formed the gang, 'Reservoir Snakes' to protect each other.
As the 'Reservoir Snakes' grew, Rosetta and Olivia began to argue about the gang's operations. Unlike Rosetta, who claimed even the weak should be protected since they are a part of the gang, Olivia considered them as useless beings who endangered it. To lead the gang down the right path, Rosetta challenges her close friend, and leader of the gang Olivia, to a duel. After a fierce battle, Rosetta was defeated, and she left the 'Reservoir Snakes'. When Rosetta disappeared, Olivia started to change the gang without hesitation. The remaining humane side of the gang from when Rosetta was a member had been eliminated. The rule of 'Members who fail their missions or lose to the enemy will be expelled immediately.' was erected during this period.
One day, Rosetta, who roamed aimlessly after leaving the gang, saves Elvira who was being chased by that very gang. Pleading that she wants to become stronger, Elvira clung relentlessly onto Rosetta. The two ended up living together under the condition that Elvira does whatever Rosetta orders for 3 days. At first, she tries to get rid of her by making her do meaningless tasks, but after realizing Elvira's genuine yearning to become stronger, she leaves behind a weapon and letter acknowledging Elvira as her apprentice.
Rosetta is considered a legend amongst Sparkling Barley Tea maniacs. Every year she participates in the 'Demon's Road' pilgrimage held in Dungeon Kingdom. Although it's the rule to participate in a group of 4, Rosetta has always participated alone saying that she can drink 4 people's worth. It is said that the surrounding customers cheer and applaud when she drinks an additional glass to rinse her mouth after completing the pilgrimage.
As for the police, she's famous for a different reason. Drunk from all the tea, Rosetta has a habit of falling asleep basically anywhere. The street, the rooftop, or even other people's beds. On days Rosetta drinks too much, you can find her in the most bizarre places. They say if you try to wake her up, she starts firing her gun randomly causing a commotion. When the sun rises, Rosetta gets up and goes on to drink tea again as if nothing happened.