Song was used as theme in one of *Kimi no Na Wa - Your name.* movie trailer. That said, it does not fit the movie so well as the movie is romantic comedy/drama.
On the other hand this is a song about people who are in *real* long distance relationship, or even separation as in the case of long term hospitalisation due to cancer or another serious illness, or war (as it was in original story).
Song was written by Nakajima Miyuki in a context of her brother suffering from lung cancer and her being unable to visit him for some reason - she was either very busy or even abroad. Her brother ended passing out the same year song was released.
Title, Subaru (昴) is Pleiades star cluster, which is known as the most famous celestial object in the Taurus, which can still be seen even in light-polluted cities. It refers to the fact that the people are still together (and can see it) even when very far apart.
There are no official English lyrics for the song, but fan translation provided online is as follows:
Shining Subaru
Is twinkling on the night sky
Even though I am not by your side
I am thinking about you
So we can smile at the same sky
In this place where we are now
I would like to find an answer
We are so close, aren't we?
Even though we can't meet
You are close to me
We are under the same sky
If the time comes when you wish
For the Pleiades to become more dazzling
I will tell you I love you
With my song carried on the wind
Shining Subaru
Is twinkling on the night sky
Even though I am not by your side
I am thinking about you
So we can watch
The same place for a moment
Let's believe that we will meet once again
The Pleiades are shining on a clear night
No matter how far we are,
We are looking at the same sky
When the day when you can reach out to me comes,
I will tightly hold your hand
Because I love you
The stars in our eyes
Are the very same stars
They are a string that connects us
When the light of the Pleiades shines
Let us cross the night of sadness
And meet again smiling
Let us believe that we will meet once again
The Pleiades are shining on a clear night
No matter how far we are,
We are looking at the same sky
When the day when you can reach out to me comes,
I will tightly hold your hand
Because I love you
Shining Subaru
It's twinkling on the night sky
I wonder if you can hear me
I'm still believing
That we’re always next to each other
Shining Pleiades
It’s twinkling on the night sky
When the wind blows on my cheek
I smile and think
When the day comes
When we cross the night of sadness
And meet again smiling
Let's believe that we will meet once again
The Pleiades are shining on a clear night
No matter how far we are,
We are looking at the same sky
When the day when you can reach out to me comes,
I will tightly hold your hand
Because I love you
Shining Subaru
It's twinkling on the night sky
I wonder if you can hear me
I'm still believing
That we’re always next to each other