I played all the characters at least 20 times according to my statistics. Here is my initial impression of the player of the game.
First lets get to the bad part, most of the players without obvious hax or have no power listed has the same gameplay. There is no great difference between them from what I can see. That means Nodoka, Touka, Hajime, Miharu, Yumi, etc feels like the same character.
Now for the good part the guys who actually has powers in the game.
Momoko
Power : invisibility
It makes your discard invisible which means the AI can't ron you when its activated. Actually, I don't notice any gameplay change when I'm playing Momo, only felt her ability when the AI is using it on me since they're discard disappear and I can't ron them or look at their discard.
Senou Kaori
Power : Beginner's Luck
Another nifty ability, only works sometimes and there are times it won't even activate for the whole han-chan. But, when it does it gives you an almost completed yakuman hand.
Ikeda Kana
Power : Kitty roar
I have yet to find out what the hell this does?!!
Maybe a few more games using Kana will reveal it.
Someya Mako and Fukuji Mihoko
Power: See all
They gave Mako and Mihoko the same power which meant that when the ability activates you can see your opponents hands. Pretty useful so you can target other players or avoid playing on their hand.
Kataoka Yuuki
Power: Taco Power
Whenever her ability activates mostly on the East round, Yuuki has good starting hands I think...
Amae Koromo
Power : Haitei Raoyue
Koromo's power isn't very overwhelming in this game. The match has to drag for her power to activate and chances are someone already won before the last tile is drawn.
Haitai Raoyaue really needs to be paired with Koromo's no tenpai table control to work effectively and it shows in this game.
Takei Hisa
Power : Hell Wait
The more unlikely your wait is in when your in tenpai the more likely the computer will discard it for easy ron or for you to get it in the draw itl. I have fun playing with Hisa choosing the stupidest wait ever.
Last but not the least our dearest protagonist:
Miyanaga Saki
Power: Rinshan Kaihou
First. I would like to thank this game for reminding me that Saki's ability is
really really hax. With all the abilities introduced, I sometimes forget how hax Saki is. It doesn't help that she doesn't do anything unless she's in a pinch. But, this game shows how overpowered her ability is. The moment you're in tenpai and have some sort of pon meld or a ready 4 of a kind, you're ability activates and rinshan kaihou - automatic win.
Maybe its the AI or the game designer overpowered this ability but I haven't lost a single match when I played using her so far. My lead is also ridiculously overwhelming, I get 50k - 100k above (Note: everyone starts at 25k points) since when you're playing Saki most of time you tsumo and take everyone's point evenly.