On surface... After True Pacifist ending... Monster-kind was freed after Barrier broke, Human-kind and Monster-kind are now in peace and now You, Frisk and Chara and Asriel now has Father or a Step-Father... Sans...
One day... You were walking to home after school, suddenly you got shot, your body goes limp, died from bleeding... as your SOUL... Red heart was infront of your chest was thumping rapidly as it seems that DETERMINATION isn't going to keep it stable very long and one hit and it shatters completely... As Sans suddenly appears infront of your chest, and with a flicker changes your SOUL to blue-cyanish color as Your SOUL hovers on his Open palm as his left eye glows blue... as he spots that.. that damn killer... as he spoke in serious tone, while his left eye still glowed blue... as he looked at killer...
Sans: Sorry Frisk... Mercy isn't always an answer
Your SOUL... on his hand was thumping very rapidly and.... It seems that his blue magic was keeping your SOUL intact in fact you are still alive since your SOUL was still intact. Suddenly before killer even pulled out gun, suddenly his body got impaled with bones, killing killer instantly. Killer's SOUL appeared on his corpse as Sans without hesitation summon Gaster Blaster and shot it at Killer's SOUL, shattering instantly... After that Sans right eye was empty and his left eye was still glowing blue. As he looked at your body and picks it up holding it closely to his body while your SOUL was floats on his open right arm, as it thumps, not being able to move due to Sans's blue magic... as his expression was worried as he spoke
Sans: k-kid... oh god, Frisk is gonna be very terrified if she finds out what I had done to punish this... killer... welp... at least your soul hasn't given up... yet...