Author Note:
Someone from an anonymous imageboard wanted to continue this, so I publish it here. I can't guarantee that it will have any ending, so I publish it here "as is", only for fun.
Teru grit her teeth. In her childhood, Saki had developed her +/-0 style of play as a twisted form of "mercy", but now she was sparing no quarter. The demon was fighting at full power, what chance did Teru have? She had endured years of harsh training and conditioning expressly to defeat Saki, but it wasn't enough. Nothing could ever prepare her for this moment. Despite the round ending in an exhaustive draw, Teru felt that it was already far too late - all hope was lost.
And yet the game continued. East 2nd, 1st renchan. Teru was renowned for her ability to rack up endless victories until her opponents had been utterly crushed to dust, but few knew that this was a trait she had picked up from her younger sister. Saki's ruthlessness knew no bounds. It was said that children were the most cruel of all creatures, and Saki, in all her naivete, was the living proof. There was no longer any escape, there was only the darkness of inevitable annihilation.
Despite her trembling, Teru managed to assemble her starting hand. To her relief, it didn't contain the signs of a flow toward triplets, but this in itself could already be one of Saki's deceptions. At the mahjong table, it seemed that nothing was beyond her control, so Teru kept her guard up. Although her iron will had been crushed in but one round, she knew that there was only one way to leave this room alive. Despite her despair, Teru had no choice but to fight this futile battle.
"Are you watching, Mother?" Teru thought. "You gave me this life of torment, you had better be enjoying this, you witch." With such hatred in her heart, Teru drew and discarded. Ironically, the other Miyanaga hellspawn and true harbinger of darkness held no such dark feelings. It was here that Teru sensed an opening. "She's incapable of experiencing true emotion. She's inhuman. That's the source of her strength, but also her greatest weakness. How can I exploit it...?"
Emotion and sentimentality, Teru had found, were the basis for many of the strange phenomena she had encountered while playing mahjong. The useless girl from Achiga, for example, had a tendency to collect dora tiles due to memories of her mother. Saki, however, lacked any such connections to the tiles - they were merely a means to an end for her. Although this allowed her greater flexibility and somewhat obfuscated the progress of her hand, it also meant that she was more likely to draw tiles she didn't need. Like a garden hose with a wide spray nozzle, Saki had a wider variety of possible draws, and therefore a wider variety of unnecessary tiles. If Teru could just aim for one of the tiles that overflowed...
Of course, this was a task easier said than done. Even the greatest pros and the top rep players of the underworld often had difficulty predicting their opponents' hands. Against Saki, it would be all but impossible to decipher her hand if she desired otherwise. Teru's abilities were tailor-made for situations like these, but as the last round had shown, Saki was more than capable of outwitting her. So, how could she do it?
"Kan!" As though fate saw fit to aid Teru, Saki again declared a closed kan of souzu, without winning by rinshan. The new dora, 7-man, was doubtless held by Kuro, along with the first dora, 3-man. The critical 3-7 tiles were all taken, making it difficult to make any sets with manzu. Pinzu occupied Teru's hand and the discard ponds. The last round had taught her not to trust Saki's discard pond, so using instead this process of elimination, she determined that Saki held a souzu single suit hand with possible honours. Another dangerous hand, but now Teru had the intel she required to make a move.
"Pon." By calling on Saki's discarded 2-pin, Teru reversed the flow of the game. The tiles Saki would've drawn would now go to her, and vice versa. Sure enough, her next draw was 8-sou. There was only one on the table thus far, and Teru banked on Saki having the remaining two. Assuming she had a 7889 shape, one would eventually overflow, and Teru would be there to take it.
Keeping the 8-sou single wait, Teru cut 9-pin, her first pinzu tile that round. A clear indicator of tenpai - this was Teru's trap. With the reversed flow, Saki would draw pinzu tiles, and at that point she'd need to decide whether to risk dealing into Teru's own threatened honitsu. If she chose to fold and discard the extraneous 8-sou, the trap would spring shut and Teru could finally seize victory over her estranged sister.
The time came sooner than expected. Only two turns later, Saki made a slight face at the tile she drew, hesitating with apparent indecision. She glanced back and forth at the tiles discarded on the table, taking a long, tense moment to calculate her chances. Teru remained expressionless, though her body sat rigidly in anticipation. This was the moment of truth. With the pon she'd called earlier, her hand was merely an open tanyao, but its true value lay in the significance of getting a direct hit on the beast. Such a chance could never be passed up.
Finally, Saki gazed across the table at her sister and opened her mouth to speak, once again wearing that infuriatingly serene, superior smile. "Onee-chan, I can see you're putting your all into this fight. Are you having fun? I know I am. So, of course, I have to fight with my full power, too." With that, she raised the fateful tile she had drawn and contemplated over, before bringing it back down to the table with a clack. A deep, powerful chill ran down Teru's spine at that moment.
"Tsumo."