This refers to Red Saber and Elizabeth.
We can’t go without saying that they are both super rare level Diva. Let’s leave the debate of whether this is a plus or a minus for another day.
Red Saber takes Elizabeth’s creativity seriously, and listens to her demonic sounding song as if it were truly intended to be demonic, as even goes as far as praising it with “That’s also good!”
But Elizabeth has absolutely no idea that her song sounds so terrible. This is because she suffers from chronic headaches which impede her from accurately grasping musical scales. At the start Elizabeth sings her extremely tone-deaf song “to make myself feel good” but eventually she subdues her selfish feelings and becomes a true diva who sings for the benefit of others.