Tekken 6

You can get this achievement very early on in the game, I got it during the level; "South Bay Warehouse Area".

As you progress through the level you'll see what appears to be a gatling gun laying on the floor, pick it up by pressing the "A" button and then use it by pressing the "X" button.

Now that you have a weapon, carry on through the level and very shortly a bunch of enemies will appear, hold "X" to use the gatling gun which will kill them and unlock the achievement for you!

* ^{Credit to RoosterTeeth for the video}

as you progress through scenario mode you'll sooner or later come across a weapon you can pick-up, simply pick it up () and kill any random enemy using ()