Determined to pursue his glorious childhood dreams, 30-year-old Rick Gladiatol, a modest clerk in the adventurers' guild, is offered a once-in-a-lifetime opportunity after he fatefully encounters the dark elf Reanette Elfelt. Reanette happens to be an elite adventurer of the legendary party Orichalcum Fist, whose members welcome Rick under the condition that he follow a Spartan training. Two years later, Rick is finally ready to take the E-Rank exam officially qualifying him as an adventurer. However, raw magical power can only be developed until one turns 20. As such, Rick faces the general hostility of fellow participants and examiners alike, leaving him no choice but to show the world that his hellish training has turned him into an invincible warrior.

Takumi Fujiwara finally joins Ryousuke and Keisuke Takahashi to create Project D. Their goal is twofold: Ryousuke wants to develop his High-Speed Street Racing Theory, while Keisuke and Takumi aim at improving their driving skills by facing powerful opponents on dangerous roads. The idea of Project D is to challenge street racing teams from other prefectures to improve both their uphill and downhill records. In order to attract the attention of the best racing teams, Ryousuke creates a dedicated website to announce the future battles of Project D and post the team's results. The fourth season of Initial D details the hardships and successes of the members of Project D as they try to become the best street racing team outside of Gunma Prefecture.

Owing to an increasing debt, Kaiji Itou ends up resuming his old lifestyle. One day, while walking on the street, he stumbles upon Yuuji Endou, who is hunting Kaiji due to the money he owes to the Teiai Group. Unaware of this, Kaiji eagerly follows Endou, hoping for a chance to participate in another gamble, but soon finds out the loan shark's real intentions when he is kidnapped. Given that Kaiji is unable to pay off his huge debt, the Teiai Group instead sends him to work in an underground labor camp. He is told that he will have to live in this hell for 15 years, alongside other debtors, until he can earn his freedom. His only hope to put an early end to this nightmare is by saving enough money to be able to go back to the surface for a single day. Once he is there, he plans to obtain the remaining money needed to settle his account by making a high-stakes wager. However, as many temptations threaten his scarce income, Kaiji may have to resort to gambling sooner than he had expected.

The Armed Detective Agency is still on the run from the Hunting Dogs, but not all hope is lost. Detective Ranpo Edogawa has a plan to prove the Agency's innocence and save the world from chaos: to find and capture Kamui—the leader of the terrorist organization Decay of the Angel. In order to determine Kamui's whereabouts, Ranpo and his colleague Atsushi Nakajima must convince Ouchi Fukuchi, the renowned captain of the Hunting Dogs, for amnesty. Although Fukuchi was tasked with arresting the members of the Agency, his past with the Agency's president, Yukichi Fukuzawa, may be the key to earning his trust. But unbeknownst to them, Fukuchi might not be as honorable as he proclaims.