I was listening to this song lately and was kinda surprised at how well it fits with Clannad After Story, especially with the lyrics. For any Shinkai fans who watched 5 Centimeters Per Second, PREPARE FOR FEELS.
Here is where I got the translation from and let's just assume for argument's sake that they are accurate since I don't know Japanese that well. I won't post the full lyrics here because otherwise, this post gets a lot longer than intended.
TL;DR: There are a lot of parallels between the lyrics of this song and a particular time in Clannad, particularly After Story . While not everything matches up and a lot of it is just common sediments that lovers or broken hearted ones say, it still is really surprising that there are these many similarities. It is almost if Tomoya himself picked up guitar lessons and sung this.
Right in the first stanza, there is a pretty obvious mirror to the events of After Story, especially Nagisa's death, and Tomoya's feelings:
"If I lose any more than this, will my heart be forgiven
How much pain before I can see you again
One more time, please don't change the season
One more time to the time when we fool around"
The first line could easily be interpreted to be Tomoya's feelings about all the sins he has and still is committing by running away from Ushio. I see it as him wondering if the more he is punished by having his family taken away (which DOES happen) that he will be forgiven, either by himself or perhaps Akio and Sanae. The second line is an obvious reference to Nagisa and the last two are even sadder when relating it to Nagisa's passing.
The second stanza has some lines that honestly sound like they were being uttered by Tomoya himself, particularly the first line:
"Making me indulge more in my selfish way
One more chance tripped by memories
One more chance we cannot choose our next place"
Tomoya has always been a selfish character to an extent, but this paints it in a far different light. This line along with the entire song highlight a lot of startling similarities in unrequited love and mourning a loss of a loved one. The line about "being tripped by memories" also plays well into the character development of Tomoya not being able to accept what has happened after Nagisa passed away at birth.
Now a lot of the song, for the beautiful imagery it uses to convey the singer's feelings, it also has the theme of missing a loved one and wanting them back more than anything. Thus, there will inevitably be a ton of similarities and I won't go over ALL of them since I will repeat myself even more. Here are a half dozen more lines that I felt have startling parallels to After Story:
"If my wish is to be granted, please bring me to you right now"
This one is obvious, but wishes are central to the story of After Story. By the end of After Story Okazaki does get his wish finally granted and while wishing for a loved one to come back, it's interesting that it is mentioned in the song too.
"I always end up looking somewhere for your smile"
Another fairly common sediment, but think back to all the times Okazaki thought of Nagisa. In the picture he frequently saw framed of her, Nagisa's smile was always visible and this is something Okazaki saw commonly when she was alive.
"If miracle was to happen, I want to show it to you right now
A new morning, myself"
Same idea like the one about wishes, but I found the second line there about a new morning interesting. While much of the song could fit in the timeline between Nagisa's death and Tomoya meeting Ushio, referring to a new morning and myself implies a change. It would fit well post meeting Ushio and be him trying to communicate with Nagisa, saying that if a miracle like many of the others that have happened were to happen to him, he'd want to show Nagisa how different and more responsible he is. If this is all to fit in the timeline of him losing her, he could also just be being sarcastic here in a jaded way, implying that every day just blends in and feels the same after Nagisa died.
"Betting and embracing everything"
Betting usually implies gambling, which I find interesting since that is exactly what Tomoya did like his father proceeding his Fathers death.
"There's nothing else that I want
Nothing else is more important than you"
This is the last line I will discuss, but this reflects the attitude of Tomoya after he lost his wife. He disregarded Ushio and in some respects Sanae and Akio since he has a lot of painful memories that are tightly linked to them. And while Tomoya was in denial and reclusing, he desperately wanted her back and it was clear by the way he acted.