Daiisshou | Hametsu No Ganbou

This was not madness. This was purpose.

If ruin was the answer, then he would become the question. Hametsu no Ganbou Daiisshou

The first crack appeared not in the sky, but in the mirror. This was not madness

He reached into the largest shard and pulled out a black flower — petals made of ash, roots made of regret. It bloomed in his palm, and with it bloomed the first note of a song that had no end. a game BGM

“Is this what you wanted?” the mirror whispered.

It seems you're referring to (破滅の願望 第一章), which translates roughly to “Desire for Ruin: Chapter One” — possibly a doujin music track, a game BGM, or a fan-made composition, given the stylistic naming.