On this page, you can learn Japanese with a Japanese song. The title of the song is Lemon by Kenshi Yonezu.
The lyric for you to learn is from the beginning up to 25 seconds in the video.
(It would have been great if it was a dream.)
夢（ゆめ）means ‘dream’. ならば means ‘if’ and follows a noun. どれほど means ‘very’. The most common word for very is とても. どれほど is not used as much as とても in a daily life.
よかった means ‘was good’. でしょう means ‘would be’.
(I still see you in my dreams.)
未だに（いま・だに）means ‘still’. It is same as まだ. あなた means ‘you’. 夢にみる（ゆめ・にみる）is a verb and the meaning is ‘dream’. あなたのことを夢にみる means ‘see you in my dreams’. It is same if you just say あなたを夢にみる.
(as I go back to get something I left behind.)
取りに帰る（と・りに・かえ・る）means ‘go back to collect (something)’. ように means ‘as’.
(I clean up the dust of the old memories.)
古びた（ふる・びた）means ‘old’. It is same as 古い（ふる・い）. 思い出（おも・い・で）means ‘memories’. の means ‘of’. 埃（ほこり）means ‘dust’. を is an object marker particle and does not mean anything.
払う（はら・う）means ‘clean up’ if it is used with 埃. 払う usually means ‘pay’. For example, お金を払う means ‘pay money’. お金（お・かね）means ‘money’.