(In this particular scenario from "A Tale of Two Sisters", everything is completely real and nothing is imagined or hallucinated either, unlike what happened in the actual movie.)
Su-mi had finally snapped after her cruel and remorseless stepmother Eun-joo went much too far this time around, by poisoning her younger sister Su-yeon for seemingly no reason whatsoever, yet it took this heinous action on the older woman's part to at last cause the protective and loving sister of Su-yeon to completely lose it, because up until now both girls had more or less put up with Eun-joo's ever increasing abuse, however things were most definitely different on this particular occasion, much to the chagrin of the unsuspecting female who would soon pay dearly for ruining the lives of her cowardly and spineless husband's daughters!
Moo-hyeon was away visiting relatives right now, because he just couldn't cope with his family's current negative situation, one in which his wife often lashed out at not only himself, but also his two daughters as well, so the supposed head of household abandoned them both and would not be coming back again for at least the next few weeks, thus setting the stage for Eun-joo to become even more violent than before, yet it would end up costing her a great deal of mental agony and physical suffering before all was said and done.
Su-mi quickly came to her sweet and innocent sister's aid just then, after discovering that poor Su-yeon had been poisoned by that disgusting excuse for a human being, and after administering medicine to Su-yeon and making sure she was alright, Su-mi at last left her sleeping sister to recover from almost being killed by Eun-joo, as she slowly walked into the living room before grabbing a flower vase, bringing it down with great force against the merciless tormentor's head, even smirking sadistically after the wicked stepmother crumbled to the floor. Sneaking up behind Eun-joo had finally turned the tables and for once the abuser would become the abused!
"This all ends for good today, and you won't ever lay a finger on Su-yeon or myself again!
Su-mi dragged her unconscious stepmother over to the basement, and after opening it up she coldly and casually shoved her down it as Eun-joo's body made sickening thuds against the steps, before finally coming to a rest on the floor. Su-mi remembered all of those terrible times that Eun-joo abused her, but the overly protective sister simply took everything without hardly ever fighting back either, because at least it meant Su-yeon would be safe from all harm, but even that was not enough because eventually Eun-joo started taking it all out on the younger, weaker and more easily frightened girl, yet up until now Su-mi never really knew about the full extent of Su-yeon's abuse, due to her frail sister hiding the truth regarding how often Eun-joo mentally, emotionally, and physically made this poor girl's life a living Hell on earth!
Cold water being splashed against Eun-joo's face quickly woke her back up, yet she was now tied up to a chair and unable to do anything about it either, as the vengeful Su-mi suddenly began zapping the already injured woman over and over again, using a powerful stun gun to torture Eun-joo as the older female screamed in agony, much to the sheer delight of the one standing above her, looking down at this wretched individual who'd caused people so much anguish over the last several months! No amount of begging and pleading could make Su-mi stop though, and if anything it only served to anger the young woman even more than before, as she reached down to grab some long, sharp scissors.
"Goddamn loud mouth bitch! Someone should really shut that fucking mouth of yours up!"
Eun-joo's protests fell on deaf ears as her abused stepdaughter slowly began cutting her tongue off, taking all the time in the world to inflict maximum damage until finally, only gurgling sounds were heard as Eun-joo coughed and spit out blood from what little now remained of her tongue!
"There, much better! Oh and I almost forgot something else too."
Quick, small cuts alternated between much deeper and more savage ones, as Su-mi used both a fillet and butcher knife to inflict dozens of wounds upon the helpless Eun-joo's body, being careful not to kill her just yet because she deserved to suffer tremendous pain for however long Su-mi so desired. Eventually she undid the ropes holding Eun-joo's hands and feet against the chair, causing the mutilated female to fall on the floor as blood gushed forth, which greatly excited this formerly kind girl turned brutal avenger, to the point where she reached down and began covering herself with Eun-joo's blood, as both hands became soaked with it before smearing the bright, red crimson all over her face and other body parts for good measure!
"Time for you to depart from this earth."
Su-mi then grabbed a large burlap sack and placed the already dying woman inside of it, which took some time because by now Eun-joo was more or less dead weight, but after this had been accomplished she began repeatedly beating the sack with a metal pipe, using the dangerous weapon to finally end this miserable woman's life, as Eun-joo's brains were turned to mush while many bones were broken along the way! She then poured gasoline all over the bag and set it on fire, laughing insanely as what remained of her stepmother burned until little was left of the corpse.
Su-mi was arrested for the murder but was declared mentally unfit to stand trial, due to her sudden and complete break from reality, no doubt the result of her mind snapping and being unable to tell right from wrong anymore. Su-mi being sent away to a mental institution was the last straw for her father Moo-hyeon, who later committed suicide by hanging himself in the very same basement which his wife had so violently met her untimely demise, but thankfully Su-yeon was soon adopted by a kind and loving family, thus bringing a mostly tragic, but at the same time somewhat positive end to this unfortunate chain of events.
