Xûr, Agent of the Nine, sometimes sells this item in the Tower.
Within Destiny 2, The Last Word was given by Shin Malphur to an unnamed Guardian in their attempt to slay a Hive Weapons Master during an exotic quest. The Guardian kept the weapon as a gift, bringing about the scrutiny of The Drifter (Character), due to The Drifter's allegiance with the Guardian and his hatred for Shin Malphur.
The Last Word can be upgraded with the following perks:
This weapon causes kinetic damage.
The weapon can be fired quickly and continuously.
Consume a more powerful Weapon to boost the Attack value of this Weapon.
Penalty to Impact.
Smart Drift Control
Predictable and controllable recoil.
Penalty to range.
More predictable recoil.
Shorter range and more recoil.
This weapon has bonus accuracy while firing from the hip.
Single Point Sling
Switch weapons faster. Move quicker while aiming.
High Caliber Rounds
Oversize rounds built to stagger targets and leave them reeling.
Their mass makes a weapon harder to handle.
This weapon has extremely low recoil.
Improved stability and target acquisition when firing from the hip.