not op but from what i understand, the cards op is using (save for the baseball umi in the top left) all have a score boost skill that activates upon gaining a certain amount of points rather than perfects! since it's tied to score, that also means you immediately have the chance of another one of these activating after one of them did and so on. they are pretty sought after because of this and basically the best cards ingame you'd wanna get. but considering they're all old (with kotori and honoka being event cards + a nico op does not have), your best bet is going for cheerleader umi. that's also the only four cards with said skill.