Early in Black Panther: New Yakuza Chapter (prologue) a man will ask you to find him 101 cats. So when you play the game, you will be able to hear cats, if you investigate and find them. You can bring them back to their owner and get a cash reward. Feels good not punching someone in the face for money!
As for Idol cards, when you are walking around Kamurocho you will be approached by Idol managers who want to promote their upcoming Idols. They will give you promo cards, each Idol has 6 cards. Each Idol is a real girl, who are also trying to become an Idol in real life. Sounds a bit sexy.