The Last Dagger is a handgun the Magisters had in their possession when they first joined Albion. Despite using small caliber ammunition, it gained in power and popularity once electromagnetic acceleration barrel technology was applied to it. However, the reason this gun is called the Last Dagger is not attributed to its powerful nature.
The once-Vulgus Magisters were never battle forces, so there was no reason for them to possess such a powerful weapon. The final order the Magisters received was to succeed in fully eliminating each other if a situation ever arose in which their intellectual property was at risk of being seized by the enemy. Thus, the Last Dagger signifies the final death blow they were expected to carry out against themselves and their colleagues.
However, when the Magisters converted to the side of the humans, they completely changed the weapon's meaning and succeeded in modifying it into a weapon for the battlefield. There were no changes from its original form in terms of power and performance. However, changing the weapon's fundamental meaning was a great challenge for the Magisters.