This is a program that takes any document with Japanese text and converts it into flashcards you can use with Anki. The default settings remove very common words and words that don't occur often in the text, but play around with the settings at the bottom!
You can give it a raw text file (including subtitle files like .srt), a web page address, or copy-paste some text directly; in any case all non-Japanese text is automatically removed. (For example, you can find many anime subtitles that should work with this here.)
Give it a second after clicking "submit," especially for larger files or webpages. When it's done processing it will download a ".tsv" file, which you can import easily into Anki with the "Import File" button at the bottom.