
Originally Posted by
Ryllharu
I don't really see the "I'm so clever I can predict your every thought" from Code Geass as a valid comparison here. Shiro has been cast as someone really amazing at games where the rules are clearly defined, but her weakpoint is that she's not very good at handling cheating or things that require leadership, charisma and bluffing. Sora is a master liar, but lacks her raw intelligence and hand-eye(& foot) coordination. That's why they are unbeatable as a pair.
A game as simple as Othello can be optimized by math. There have been computerized versions able to beat very good human players since the 1980s. The two are certainly good enough to recognize how the other would play, and now that I actually think about his strength, Sora would be an expert at forcing Kurami to play the way they'd want through bluffs and misdirection (as he has been shown to use often). Shiro would know what moves he intended to force Kurami to make.
He set himself up for apparent failure so that Shiro could finish it for him. Othello is a game where the tide can completely turn in just a few moves. You sort of have to lose a little to gain back a lot.