I think I like this song, but I don't speak Japanese. Looking at this translation, I wanted to make it look like an English poem. I know it's not perfect, but here is the result:

We all know magic will end someday
The moon blooms, but the sun withered in decay

Your umbrella is held out for me
And in its reflection, there I see
My dry face staring out of it
But in the puddle, my reflection's wet

Is joy causing my tears to flow?
What is this feeling? I don't know
It was raining in my dream
I wake to find that my eyes stream

A rainbow spreads across the gray
Of the clouds, but it will fade away
But under where it was, below
Down there, the rain still makes plants grow

Rain falls where the rainbow spreads
When the rainbows gone, we still lift our heads
To see where its colors once flew
And our gaze might always continue

In the pure white of the night
A train's shadow against the light
It passes on and we remain
In the quiet, in the rain

Oh! I want to run away
My heart is dancing. Must I stay?

What is this feeling that I feel?
Is my reflection like it was, still?
When I turn from mirror glass
Sometimes it seems like ages past

A rainbow spreads across the gray
Of the clouds, but it will fade away
But under where it was, below
Down there, the rain still makes plants grow

On a day like this, I won't forget
How, as it rained, we gazed together at it

A rainbow spreads across the gray
But I know that it will fade away
But water on the earth below
From the rain is causing plants to grow

And if, one day, the rainbow's gone
Expectantly, we'll still gaze on

Finally, when the showers end
And the flowers bloom in the garden,
I'm thinking now that it's okay
And planning our next rainy day