那一天

「

Kris.
... ever since that horrible day...
I've... only blamed myself for what happened.

」 ——Asgore, Chapter 5

That Day is the 35th track of the DELTARUNE Chapter 5 OST. It plays during Asgore's flashback scene, after the battle with Flowery.

In the cutscene, Asgore notes about a horrible incident that led to his self-hatred and obsession to prove that the incident was not his fault, leading to the events of Chapter 5.