This is used for the 14th ending theme of Naruto Shippuden.

The story of the lyrics revolves around a girl, now grown up, who reminisces of a summer day in the past. She went together with the boy she was in love with to a summer festival. While the fireworks went into the air, she stole a glance at the boy's enraptured face as he saw the fireworks with joy. As they were resting on the roadside laughing and enjoying the fireworks, she was able to present her feelings saying "I love you" and they kissed. But that was the last day she ever saw him, never to meet him again. A transient moment with him it was for her, one that she feels she regrets.

AniDB | MAL

Other: Naruto Shippuuden