Hiroe is Hisa's estranged former Middle School teammate.
Hisa withdrew from the Nationals in Middle School because of her parents' divorce.Her name changed from Ueno Hisa to Takei Hisa after this...Not much to really explain here, is there?
Jindai pushed herself too hard in the previous year's tournament fighting Teru.In Chapter 56 of the manga, Hatsumi mentions how all of the Kagoshima family branches have sent representative players for this year's tournament for the purpose of helping Jindai, who had pushed herself too hard the year before, and is already rather frail. Jindai serves as the Vanguard (First player in a team tournament) for Eisui - The very position that Teru plays for Shiraitodai. And since Teru is heralded as the world's Number One player, and an extremely powerful opponent to boot, it doesn't take much brainpower to infer a causal relationship from here.
Saki can reunite her family through MahjongIn a Heart of the Stones way. Seriously, with all the Super Powers around, we are definitely in that kind of setting.
Hagiyoshi is a ghost.I don't think it needs much explaining as to why I think this.
Saki indirectly caused her family's break-up, which caused Teru's resentful attitude of her, as well as Saki hating mahjong as a result.I'm surprised that after this long, no one's put this one forward yet. Not a personal theory (the theory itself originates from Triple_R+), but given the setting incredibly likely as well, given how people treat Mahjong like Serious Business on the level of The Legend of Koizumi: The Miyanaga sisters' talent with mahjong was obvious at an extremely young age. This really excited their parents, and made their parents want to do everything they could to see both daughters become successful pro mahjong players. Saki once mentioned that if she came in last during mahjong games with her family, she'd "lose her New Year's money" or something like that. This hints at how seriously the Miyanagas took mahjong - even to the point that monetary incentives were put on the table. This may have been the Miyanaga parents' way of trying to push their daughters forward into being better mahjong players. Now, perhaps Teru thrived under this pressure (or accepted it, at least) while Saki chafed under it. Saki didn't like how intense these Miyanaga family mahjong matches were - They weren't any fun to her due to all the pressure surrounding it. So while Teru pleased her parents, Saki stopped trying to win and adopted her plus/minus 0 approach as a coping mechanism. Once Saki's parents noticed this, they became upset with her. One thing to keep in mind here is that, in real life, the parents of sports prodigies can be rather insane about it. Not all such parents are like this, but many are. Perhaps Saki's parents (or at least her mother) were similarly insane about it. Since Saki is living with her father, but not her mother, it hints that Saki's mother was the person must bothered by Saki adopting the plus/minus zero approach. Perhaps Saki's father eventually accepted, regretfully, Saki's decision to not try to be good at mahjong, while Saki's mother was incensed by it. So the two parents argued over Saki, which may have played a key role in their separation. From Saki's perspective, mahjong tore her family apart, which is why she started out hating mahjong way back in the first episode of Saki's original season. From Teru's perspective, Saki tore her family apart. If Saki had simply tried to please her parents like Teru herself did, the family would never have broken apart. And so Teru no longer considers Saki her sister; perhaps Teru views Saki as someone who dishonorably disrespected their parents' wishes, so family ostracization is called for. While Saki blamed mahjong for splitting her family up, Saki also knows how Teru blames her for it. Saki also knows that Teru isn't necessarily wrong - Maybe if Saki had tried more to keep being good at mahjong, the family break-up never would have occurred. So Saki is privately living in deep guilt, and can't face her sister at all given the shame that she feels. Saki's one hope is that if she competes head-to-head with Teru at mahjong, in an official competition where it really matters, perhaps Teru will forgive her based on clear evidence of how Saki is embracing mahjong again. One other thing that fits nicely with the theory here is how, back in Season 1, there's a brief scene of Saki's father talking about throwing out his long-unused mahjong table. There's something vaguely melancholic about that scene, and if mahjong is what tore Saki's family apart, then her father feeling a certain bitterness towards the game itself would make sense.
Saki once served as her family's sacrificial Butt MonkeyThis works similarly to the (excellent) sports theory above, but it focuses on the New Year's game as a stress reliever for this family that was already fractious. When Saki refused to be the happy bottom of this unfair totem pole by losing/getting 'punished', she finally undid the ripped seams that held them together. This family seems to attend the same school of logic as Mayu's mother from Elfen Lied, and one hopes Saki ultimately lets Onee-Chan have it with both sets of tiles.
Saki will succeed in reconciling with Teru, but won't bring her parents together againIt's most likely that Saki, by reaching out to Teru through Mahjong, will be able to get Teru talking with her again, enabling them to work out their issues. However, it's possible that this may not have the same effect on her parents, who may remain separated, although it's possible that if Saki and her mother are at odds, they too may reconcile.
Saki is a tribute to CLAMPIf you look closely you'll notice that most Saki characters look like CLAMP Characters: Yuui is similar to Sakura (Cardcaptors) and Tamayo (Angelic Layer), Kyoutaro has an Angelic Layer-styled hairstyle, Mihoko is kinda similar to Chi from Chobits. These may be clues that Ritz Kobayashi is a huge CLAMP fan.
Kuro will throw a wrench into Kiyosumi's plan to adjust Yuuki's playstyle by discarding a dora tile againThe Rinkai team notices after the vanguard match that Yuuki chose to focus on speed, at Hisa's suggestion, to counteract Kuro's ability to attract dora. Since Kuro has learned the value of discarding dora at critical moments and Harue has the ability to analyze other team's play styles, it's likely that Kuro will discard a dora tile, possibly in the hopes of disrupting Kiyosumi's plan or otherwise throwing them off. Given that Kuro only discarded her dora tile at the end of the game, and Nodoka, the only one to hear about the drawback to doing so, doesn't believe in the occult, it's likely that she didn't report that to Hisa.
Nodoka's father will still make Nodoka switch schools after she wins the tournamentIf he operates mainly under the belief that mahjong is a game of luck, he's unlikely to change that view if Nodoka wins, possibly dismissing her as just lucky. The series would likely end with Saki and the new Kiyosumi team (with Maho and Hiroko to replace Nodoka and Hisa), much like the Achiga girls, setting out once again, hoping to reach the nationals and see Nodoka again.
Saki suffers from Bipolar Disorder (aka Manic Depression).If you pay attention, you'll note that Saki has "good" days and "bad" days. On the good days, she can be extremely hyper, runs and darts around really fast and easily does things like hugging Nodoka, which she is normally too shy for. Then there are other days where she seems to have trouble dragging herself out of bed and moves in an almost zombie-like state or just sits around catatonically. She also seems more prone to depressed thoughts and tearful outbursts in these moods. Admittedly, almost everyone experiences some mood swings throughout the days, but Saki's seem a bit too extreme to be healthy. Most of the time, she seems to function well enough to not warrant immediate intervention, but if it wasn't for the fact that there are no therapists in TV land, she probably would be getting some medication and/or therapy.
Rinkai will get eliminated as a result of one of their opponents going under 0 while they're not high enough to advance.Given that's how Megan Davin was able to prevent "Cold Touka" from advancing the previous year, and that they're poised to do this again to Kiyosumi with Usuzan as the target, it would be a nice case of Laser-Guided Karma.