Japan, 1995. After graduating from high school, Itō Kaiji moves to Tokyo to get a job, but he fails to find steady employment because the country is mired in its first recession since World War II. Depressed, he festers in his apartment, biding the time with cheap pranks, gambles, liquor and cigarettes. Kaiji is always thinking about money and his perpetual poverty frequently brings him to tears.

Kaiji's unrelenting misery continues for two years until he is paid an unexpected visit from a man named Endō, who wants to collect an outstanding debt owed to him in Kaiji's name. Endō gives Kaiji two options - either spend ten years to repay this outstanding debt, or board the gambling ship Espoir ("hope" in French) for one night to clear the debt. Using a con, Endō pressures Kaiji into accepting the deal, believing he will never come back from the voyage.
--Wikipedia

The manga is divided into three parts:
Part 1: Volume 1-13 (Complete)
Part 2: Volume 14-26 (Complete)
Part 3: Volume 27-39 (Complete)
Part 4: Volume 40-? (Ongoing)

A direct sequel to Tobaku Datenroku Kaiji, picking up immediately after Part 3 ends. After his tremendous victory in 2-Player Mahjong against the villainous President, Muraoka Takashi, Kaiji is being driven home by Kazuya, the son of Chairman Hyoudou. However, in the car, Kazuya asks Kaiji if he would be interested in one more gamble that night, and Kaiji accepts. What surprises lie in store for our dear Kaiji, and what will the gamble be?!

44 years old, single, working in a construction company for his entire life. All Kurosawa wants is a little respect from his co-workers. And a little popularity won't hurt. Unfortunately Kurosawa's plans fail miserably from time to time and one day, he finds himself right in the middle of a fight against...delinquent middle schoolers?

Itou Kaiji is a bum who steals car emblems and slashes tires on what seems to be a regular basis. This routine changes one day when he is paid a visit by a man in a trench-coat. Once the two get talking, it seems that the visitor (Calling himself Endou) is a debt collector. The reason for his visit is an unpaid loan which kaiji had previously co-signed for a work-mate (Furuhata Takeshi). The original loan was 30000 yen and once Takeshi had disappeared, the loan then fell on Kaiji.
Kaiji is then told of a way to clear the interest compounded debt (which stood at 3,850,000 yen), which involved getting on a boat with others in his position. Once on the boat the debtors would then have to gamble with loaned money, which would end with a few winning, and others getting into deeper debt and having to work to pay of their debts. After some coercing kaiji accepts a position on the boat, in order to clear himself and make a bit of money as well...
(Source: AniDB)

Ukai Rei saves three troubled teens from a Suicide Website, and together they choose to work as modern-day 'Robin Hoods' of society. However, Rei's friends are caught by an underworld gang whose heist the group had foiled. In order to rescue them, Rei is forced to enter a gambling competition hosted by a rich, rotten old man who is looking for a talented gambler to be his rep player in an upcoming gambling tournament for millionaires from all over the world. The reward money? ONE TRILLION YEN.

Note - This story is directly continued in its sequel.