This game is a great way to burn time but somewhat repetitive. I managed to beat the campaign without any problems. Heres what I did-
Primary: Energy Saber(increases chance of 2x turn)
Secondary: GR-12(most accurate handgun)
skill 1: flashbang
skill 2: precise attack
skill 3: speed boost
Upgrade power until 1/2 to 3/4 full. Then dedicate all points to agility. Once agility is maxed, finish maxing power. Then max resistance. You will probably beat the game before you get to max resistance. Heres how to beat the enemies during the mid to end game(when agility is maxed).
First and foremost, start every battle with flashbang->speed boost->precise attack. Do not repeat this process once it is already done. Speed boost is permanent. Then do the following:
yellow/green/no seal: flashbang->primary attack->flashbang->precise attack(then repeat)
red seal: primary attack->precise attack(then repeat)
blue seal: secondary attack->flash bang->precise attack(then repeat)
You should beat the game at around level 30-35. Final level is act 3, mission 4. Last enemy has no seal and 400hp. Terrible ending(you'll see why).
Cheers