From the main menu, go to COLLECTIONS then EX OPTIONS. Purchase AI PARTNERS as early as you can, then set it to maximum.
In CAMPAIGN, go to ZONE 1 STAGE 1 and you can let the AI complete the stage to earn credits for you. You just need to press Y each time the stage is complete to restart it. Use credits to purchase all EX OPTIONS for achievement.
If you are not consistently getting a rank of B or better, go back to ANDROID SELECT and re-select a character. You can do this to randomize the AI selections until you get a better team.