Japanese flashcards should not become romaji flashcards by accident. Romaji — Japanese written with the Latin alphabet — can help beginners search and pronounce words. But the thing a Japanese learner needs to own is the Japanese writing system itself: kanji, hiragana, and katakana.
That is the first Japanese rule: keep the Japanese form primary.
Rule 1: Put Kanji And Kana First
Japanese words can appear in kanji, kana, or a mix of both. 食べる ("to eat") uses kanji plus hiragana. ありがとう ("thank you") is written in hiragana. A flashcard should respect that written form.
For kanji words, the reading matters. A student studying 大きい ("big") should see that the reading is おおきい (ookii). The kana reading is not a hidden search alias. It is part of how the word is learned.
Japanese kanji flashcard
Rule 2: Use Romaji As Support, Not The Main Card
Romaji is useful for search. A beginner may type taberu and expect to find 食べる ("to eat"). That should work. But the review card should not quietly turn into taberu on the front. If it does, the student practices Latin letters instead of Japanese.
The better setting is optional romaji. Beginners can turn it on. Students who already know kana can turn it off and keep the card visually Japanese.
Japanese beginner support
Rule 3: Do Not Duplicate The Same Word
Japanese data often has both a kanji form and a kana form for the same learner concept. 食べる and たべる can point to the same verb. Sometimes the kana-only form is the normal written form. Sometimes it is just the reading of a kanji-primary word.
The flashcard system has to choose carefully. If the kanji form is the form students should learn, the card should show it and keep the kana searchable. If the word is normally kana-only, the kana form should stay primary. That is a display decision, not just a search decision.
How Ludus Applies These Rules
Ludus separates the visible word, the kana reading, and romaji. Search can accept kanji, kana, and Latin letters. Review can stay focused on the script the student is studying.
That makes Japanese flashcards less noisy. The learner sees 大きい, gets おおきい when support is useful, and does not have the whole card reduced to ookii. The point of a Japanese flashcard is to practice Japanese.