Tenshi, Ei-chan, and Shiratori all attend Kawagoe Academy. One day, they get pulled into the orbit of former conductor Haruo. He drags them into his newly founded boys choir where they suddenly find themselves performing a song in front of an audience!

It won't resonate otherwise.
Not literally or in people's hearts.
لن تتردّد بخلاف ذلك، لا حرفيّاً أو في قلوب الناس
Klänge aus dem Mund allein
hallen im Herzen nicht wider.
Con la boca solo no resonará.
Con la boca solo no resonará.
Une bouche, c’est pas assez
pour atteindre le cœur d’autrui.
Se esce solo dalla punta della lingua, non risuona!
Usando só a boca, ela não se projeta.
Иначе резонанса не будет. 
Ни буквального, ни в сердцах людей.