Japanese lyrics lean on what is left unsaid. Subjects disappear, lines end on soft particles, and a word can be written in a way that hints at a second meaning. Japanese and English are already set in the translator above, so paste the lyrics as they are written and you get a faithful English translation, a singable version and notes on the wordplay.
Japanese songs give a note to each mora, a beat of sound that is often shorter than an English syllable. Tokyo is four morae in Japanese (to, u, kyo, u) but two syllables in English. That is why English versions of Japanese songs can feel stuffed or empty: an English line usually needs more words than a literal translation would use to fill all those notes.
Japanese can go through a whole chorus without saying I or you. English needs pronouns, so the translation has to decide who is speaking and to whom from the rest of the song.
Japanese has several words for I and you, and the choice says a lot about the singer. Boku is gentle and a little boyish, ore is rough and confident, watashi is neutral or soft, and kimi is an intimate, often poetic you. All of them become I or you in English, so the notes mention it when the choice shapes the character of the song.
Lyricists sometimes write a word with one set of kanji and sing it with a different reading, so the page shows one meaning and the ear hears another. Homophones are common too. Paste the lyrics the way they are written, and when the translator spots a double meaning, the notes explain both sides.
Words like yuudachi (a sudden summer evening shower) or sakura set a season and a mood in one stroke. A literal English word often sounds flat, so the faithful version spells out the image and the singable version looks for something that carries the same feeling in fewer notes.
Two original lines, written for this page, with a pronunciation guide. The first line has 16 morae and the second has 17.
夕立のあとで 君の声がした
Pronunciation: yuudachi no ato de kimi no koe ga shita
傘はもういらない 二人で歩こう
Pronunciation: kasa wa mou iranai futari de arukou
After the evening shower, I heard your voice,
we don't need the umbrella anymore, let's walk together.
When the summer rain was over, I could hear you calling me
we won't need the umbrella now, so let's walk on together
Yuudachi is a sudden summer evening shower, so the faithful line spells it out and the singable line uses summer rain. Each mora usually gets its own note, so the singable lines run to about 15 syllables to fill melodies written for 16 and 17 morae. That is why they add calling me and walk on. Futari de means the two of us, which together carries in English. Kimi tells you this is an intimate you, which English leaves to the tone.
Paste the lyrics the way they are written in Japanese, with kanji and kana. Romaji works too, but it loses the kanji that tell words with the same sound apart, so a few lines may come out less accurate.
English sentences need a subject, Japanese ones do not. The translator works out who is speaking and to whom from the whole song, and when a line is truly ambiguous, the notes say which reading it chose.
It catches many of them, especially homophones, unusual kanji readings and seasonal words, and explains them in the notes. Wordplay that only exists in how a line is sung, not in how it is written, is hard to see from pasted text, so compare the notes with what you hear.
Yes, that is what it is for. Each line aims to fit the same melody and keeps rhymes on the lines that rhyme. Japanese melodies give a note to each mora, so sing it through and adjust any line that feels rushed. If the song is not yours, releasing a cover with new lyrics may need permission from its writers or publisher.
Anything already in English is kept as it is, and only the Japanese is translated. Katakana loanwords are translated by what they mean in the song, which is not always what they mean in English.