The logic behind them was relatively simple, after all. Besides, they would be able to find where those were, and Rain would be able to teleport to where they were and destroy them.
"The machine gods are still operating under some restrictions, so they won't come to destroy us if we create that… at least for a while," Rain thought. "Anyway, the planet had enough mana for that since the overseer can keep the barrier that separates the layers… that being said, using our own mana for that should be the best option."
For the defense system to work, the group needed a bunch of things. Aside from crafting a big enough cannon that could store that much energy, they also needed to make it work automatically after sensing a powerful attack approaching.
"... We should be able to save some mana and gain piercing power by using a mana gem as a projectile and making it explode," Rain thought.
My Legendary Weapon Can Evolve Infinitely!