huh?
when was this ability a thing?
It was in the early chapters that the Lovers Arcana can develop new magic spells.
It's how he learned the ultimate fire spell Fidezenon to beat the first mook. It's also how he was able to complete the world destruction spell in class to defeat The World.
Regarding Miyabi, it's... not adapted the best, but all his cards have unique bloodline abilities. Basically how when the Devil Arcana picked that other guy he got that crazy mind control ability, the other demons also have latent abilities.
If another person got the Devil Arcana they wouldn't develop the same ability.
That's why it's special that the Lovers arcana chose a human in the story.
Miyabi wasn't chosen as a card holder however so her family's latent ability never manifested.
Devil Arcana knew that Miyabi's family's latent ability is the only thing that could counter his own. The power to duplicate abilities, which is why he targeted the subfamilies and other servants of the Yuugaoze family. It's why they're in ruin.
Cause of the blood passing between them in the last kiss, the Arcana used Miyabi's blood, to duplicate Devil Arcana's power and letting the MC sever it.
....
Basically, they've been building up to this since Miyabi's subfamilies got caught by Ibiza, and this is the reason why she's been targeted by him from the start.
I don't know how you'd adapt this part of the story properly though. When I was reading the Light Novel it wasn't so confusing, but that's because light novels are expected to have text, so they had time to write stuff out. The manga's focused more on the ero and action so it can't do it as well.
And well.. the translation's slow so a lot of readers are forgetting stuff.