The trick is using the insane amount of times you can spin to do all missions and use the pero from cards to buy gacha tickets. Always use your wilds on 1 card at a time, preferably the one with the highest sed, that way when you use the gacha those cards will level up cards of a higher rarity (doesn't happen every time, usually levels up one of a similar rarity) and level your cards up faster. After the n cards have been maxed though it doesn't work as well as the gacha starts giving you wild cards. Be warned though it will take a long time to burn through that stamina. Not to mention there are girls in the regular stages that don't appear in the gacha so it will take a while to get those.