I want to know what background music (especially light music) should be used for the true story behind gratitude.

All the time (it's piano music, even if I don't choose it, I must listen to it, really)

Anne Wonderland (Bandari)

This is a piano episode by Conan. Don't stop listening because it's Conan. You won't regret it. Very in line with the theme)

Kissing the rain (a classic piano piece you must have heard)

Angel of sadness (in line with your theme)

That summer (you know, it was Master Joe Hisaishi's summer).

Songs from the secret garden

Goodbye police (humming version and pure music version)

Tears (nice, faint sadness)

The Original Scenery of Hometown (Classic)

Ye Chun from Bandari.

Forrest Gump (Forrest Gump)

Ludlows (The movie soundtrack of Burning Years is good)

A letter to my mother (in line with the theme)

If love has providence (there are singing and pure music versions)

The street where the wind lives (erhu and piano meet the theme)

I won't forget (I may not find any sadness on Jiuku)

Youth is a person sitting on a train that never looks back (nice).

The above suggestions are suitable for everyone.