After Sans killed Frisk for some time, he used his full power and the other souls to kill Frisk. But he heard something and he prepared to attack Frisk again...but...it was you...the other soul...and you were weakly walking to him...it seemed like Frisk got to you and you tried to hurry to Sans.

“K-Kid! What happen to ya? Goddamn you were beaten bad...”

As Sans held you in his arms you weakly said: 't-take m-my s-soul...p-please...C-Chara w-wants i-it...' Then you took your soul out and held it out as your body turned to dust.

“Kid wait!!” But it was no use...you were gone...Sans looked at your soul and monsters couldn't obsorb them, they needed to eat them, but it wouldn't harm them, then Sans held your soul in his hand and puts it in his mouth and swallowed. Then he felt all the power in there.

“..a-ahh...f-fuck...h-holy shit...”

It was a lot of power, more than Sans could handle, but he manage.