Got this along with surviving 30 minutes in the Bone Zone as my last two achievements in this game.
You can do what I did and turn on "endless mode" if you lack confidence in getting enough kills in time, or just don't won't risk repeating the process. Though I didn't really need to, as by the time 30 minutes had passed, I was already well ahead of 100,000 kill mark.
Didn't even need to do anything (not even move) by the time I evolved all my weapons. If you fully upgrade Sigma's starting Victory Sword as well as Torrona's Box, you can also get the Sole Solution from a chest as a seventh weapon (provided you already have the maximum six). As the final level of Torrona's Box increases Curse (enemy stats) by 100%, best to do what I did and save its final level up till last. By then it shouldn't matter if the enemies become twice as strong, as I was now making over a hundred kills per second without even having to move!
EDIT: You must get the achievement for completing the entire collection before you can play as Queen Sigma.