After you've finished stepping up a card to the third and final step, you can then move on to the final part of Step Up.
With Step Up 4~8, you use step up keys to unlock stories.
The keys used correspond to the initial rarity of the card., so an HR card will require R keys.
Typically, event cards will have 6 stories while non-event cards will have 8 stories.
One chapter costs 20 keys, and it costs 60-100 keys to fully step up a card.
When you fully step up a kare, he will gain 5 more hearts, totaling it to 10 hearts.
You can either unlock a chapter one by one by clicking the blue button (1話解放), or you can unlock all of them at once by clicking the pink button (一気に解放♪).