system
Given the following post, respond as if you're commenting on Reddit:
human
[Pacific Rim] Why didn't the Precursors devise a more "implicit" kind of weapon, like advanced virus or mind control?

Did it have something to do with their culture?
Yes, at some point of the war they tried to infiltrate the mind of an important figure, yet they still use their beloved kaiju just to blow up Mount Fuji.
gpt
The Precursors' plan was thus: Get a Kaiju through the Breach and onto Earth, make the Kaiju jump into Mount Fuji, and the subsequent reaction between the Kaiju blood and the volcano would spew toxic poisons into the atmosphere, killing all of humanity and terraforming the planet to make it suitable for the Precursors.  

*(This does raise the question of why Kaiju starting out in the middle of the Pacific and heading to Japan would end up attacking places like Sydney, Anchorage, and Hong Kong, but let's just assume the Kaiju didn't know where Mount Fuji was and never stopped to ask for directions.)*  

Thus, from the perspective of the Precursors, there's no need to implement complicated plans like a special virus or mind control.  They just need to keep sending Kaiju until one makes it far enough to jump into the volcano.  They had plenty of "spare parts" to make Kaiju, and they could keep sending Kaiju through the Breach at increasingly higher frequencies.  It was just a matter of time before one of their Kaiju found its target.  

Granted, Gipsy Danger managed to make it through and then blow up the Breach, so that sort of threw a Jaeger-sized wrench into their plans.  Fortunately, though, they had a connection into Newt's head thanks to his injudicious decision to drift with a Kaiju brain, so that's what they decided to use for their second attempt at Earth.