It's a manga and also has TV adaptations in Japanese and Korean. It's about a guy who's a genius and has jist come out of prison for fraud and a girl who's overly trusting, who both enter a series of games where if they lose they will fall into massive debt with an underworld organisation. The games they play are all games which at first glance appear to be down to luck, but actually can be won by logic, lying and psychological manipulation. It's shares similarities with Kaiji, Akagi, Money Is Life, One Outs and Death Note, but it's a bit more complicated and precise (largely due to involving more maths) than most of those.