Details
Quote stickers are the entry point
The $7.99 tier is where most people start, and the Bookish Quote - The Cruel Prince (Holly Black) Sticker | The Cruel Prince / Holly Black is the cleanest example of what that search looks like in product form. It's built on the text of the series rather than cover art, printed with vibrant, lasting color on a die-cut sticker. Cheap enough to buy two. Small enough to slap on a Kindle case, a water bottle, or the back of a laptop next to a dozen others.
There's a second sticker at the same price: the by you i am forever undone - Cardan Greenbriar Sticker | The Cruel Prince / Holly Black, which takes the single most-quoted line in the trilogy and pairs it with Cardan's full name. Fans type that exact lowercase phrase. Not "Cardan quote sticker." The phrase itself. That distinction matters more than any keyword list, because it tells you the buyer already knows the books and wants the line honored properly.
Cardan carries the character searches
If you look at what people type after the series name, Cardan Greenbriar shows up more than anyone else - more than Jude, more than Madoc, more than the Court of Shadows combined. He's the reason the High King of Elfhame gets his own row of products.
The Cardan king of hearts T Shirt | The Cruel Prince / Holly Black at $29.99 leans on that: the king motif, the heart, the fact that Cardan spends three books being the worst possible person and then writes a letter that ruins everybody. The design reads as plain cool to a stranger and as a gut punch to anyone who finished The Queen of Nothing.
Pair shirts beat single-character shirts
The other pattern: people search for Cardan and Jude together. The Cardan and Jude, king and queen T Shirt | The Cruel Prince / Holly Black, also $29.99, points straight at the trilogy's ending - Jude as seneschal and queen, Cardan on the throne of Elfhame, the two of them bound by a bargain that turned into something neither of them planned. That's the search that says "I finished the series and I have feelings about the last chapter." Both tees sit at the same price, so the choice comes down to design, not budget.
What nobody searches for
"Generic faerie court apparel" gets zero volume. "Bookish fantasy gift for reader" gets zero volume. The queries are character names, exact quotes, and "cruel prince" plus a specific object - sticker, shirt, tote. Merch that skips the quote and the character is competing on cover art alone, and cover art is already everywhere.