I have been using WaniKani for a while now and love it. The only thing I really miss is writing practice.
That’s why I have been coding a little script (available here) to generate PDFs for writing practice based on WaniKani’s levels.
This image shows an example page of the PDFs generated. If you want to tinker around with my code, feel free to do so. In case you just want to download the PDFs, you will find them here.
I hope it helps you a little.
Have fun and cheers.
EDIT: I also made a cross-post on reddit.
UPDATE May 5th, 2015:
I added some code to generate vocabulary writing practice. The sheets only contain kana and meaning and you have to fill in the appropriate kanji.
Download Kanji Writing Practice
Download Vocabulary Writing Pratice
Update May 1st, 2017:
I have updated my code to generate the PDFs and re-uploaded them to GitHub.
Please go here to download the files: http://suchmaske.github.io/WaniKani-KanjiPaper/#/