She finds her first love at a concert twenty years later: the promise they had not forgotten

At 18, you make promises in the firm belief that you will keep them. Then life passes, everyone goes their own way, and some memories slowly fade. Or so we think. Because sometimes, an unexpected evening is enough to bring everything to the surface — and reveal what we thought was lost forever.
A promise of youth, buried in the memory
At 18, you pronounce words with absolute sincerity. That evening, after their last shared concert, they had set themselves a slightly insane challenge: if twenty years later they were both alone, they would come back. Same group. Same city. Same emotion.