If, after your daily review of due cards, you want to do more reviews, anki gives you the possibily of reviewing with custom decks, based on different kinds of options. Like cards failed most frequently or things like that. Or, you can take a japanese website, book, anime subtitles, and use it to review kanji. I don't know if what you do is detrimental per se, but I think you can spend the same time in a better way! (just my 5 cents 
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