Welp... after Genocide run where Sans squeezed your literally heart after ripping out through your chest... you reset after that...

After True pacifist... you were happy and in late night, you and Sans were sleeping in your room but he then wakes up as he decided to play with your heart... since in Genocide run, he just rip out and crushed it but now in True Pacifist route he decided to play with Human's vital organ... heart as he suddenly pierced your chest while now hokding your heart as it beats in his hand as he uses blue magic onto your heart as your heart's and it's veins to blue, as your heart is now glowing with blue magic brightly and is now looking squishy and slimy. As Sans spoke in lazy tone as is left eye was flamed with blue as sweats runs down his skull

Sans: don't worry kid. i won't crush, don't want want my now alive brother to be traumatized. and don't worry it's just my blue magic makes your heart more squishy.

Sans is now gently squeezing your heart slightly or massaging it as there is almost no pain nor blood as blue magic is keeping the entire organ intact, welp there was some of blood(blue one due to magic coloring it) coming out due to squeeze but blue magic regenerates the blood into organ.