I'm playing a VN and I've created a lesson and as I'm playing, I'm adding vocabulary with kanji that I do not know in the lesson, so I could study and review them using renshuu. I selected the study vectors that only uses kanjis, and renshuu is telling me I cannot study them because I "have selected only kanji-related questions, and some terms do not have kanji that you know." What can I do to be able to create a quiz/lesson/anything with kanji words that "I do not know" and be able to study them?
You have two options #1 - I would recommend adding the non-kanji vectors to the schedule. But, if you only wish to study ones with kanji in them, then....
#2 - Go to settings (profile icon in the top right, then settings icon). Go to Vocab. You should see "Show unknown kanji like this" - try setting that to either the middle setting (which will show the terms in the kanji vectors IF you know at least one of the kanji (the other will appear with furigana), or the far right option, which disregards your kanji knowledge for the quiz and forces the kanji out.