All that's left is the God of Hyperdeath and a scorched ring. Frisk's soul floats in his paw, shaking and threatening to burst. Just like when Chara died and he absorbed their soul. But he won't be a single entity with Frisk; he didn't have a monster soul to be transformed. The scarlet heart centers itself in the goat monster's chest, pulsing with a warmth he hadn't felt since he broken the barrier.

Asriel finally had his own soul. Had it not been for outside factors--preventing them is the whole reason he's doing this in the first place--he'd live a normal life again.

Of course it happens like this.

frisk i'm sorry good god i never wanted this happen please understand i had to do it i must there's no other way it's okay i'm going to SAVE you i'll be so powerful i won't need your soul anymore you'll be brought back and get the happiness you deserve i'm sorry i'm sorry please hold on i'll take care you it'll be all right i'm sorry i promise

His breath shakes as tears stream down his cheeks, and his lips curve into a weak smile.

You should be smiling, too.
Aren't you excited?
Aren't you happy?
You're going to be free.