It's a song with a slow tempo, and one of the lyrics is "I'm traveling alone and I'm walking." That's the song.

It's "Leaves" by San

Leaves are wings that don't fly

Wings are leaves that fall in the sky

Heaven wasn't supposed to be a delusion

It's just that I've long since forgotten

How to fly in the first place

Loneliness is the revelry of a single person

The revelry of a group is loneliness

Love starts as companionship, but I too have gradually forgotten.

But I've gradually forgotten

How I was accompanied

I ate and traveled alone and walked everywhere

I also read and wrote letters alone and talked to myself

It's just that my heart drifted away to wherever it went

I couldn't even see it for myself

I think I didn't only lose you. I've lost you.