As ekg mentioned, I wrote a userscript that does similar to what you’re asking for. It displayed WaniKani’s vocabulary for the kanji on the review page:
Purpose
These past few months year, the number one thing I’ve spent my WaniKani time on has been book clubs reviewing the same leeches over and over and over again. No technique has been completely successful at combating these leeches.
However, one recent technique has shown great promise for improving my kanji reviews: adding vocabulary words to the review screen. Having this vocabulary list has doubled to tripled my review accuracy for my kanji leeches.
To streamline this, I’ve put the lo…