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. [Written by MAL Rewrite]

Akebi Komichi lives out in the countryside with her family. She's won entrance to the prestigious Roubai Academy middle school for girls and now she wants only two things—to wear the school's sailor uniform and to make a hundred friends!

Kio is just another boring, nice guy with a boring, nice life until he meets a beautiful, curvaceous cat-girl while attending a memorial service for one of his ancestors. Next thing he knows, he's lying in bed with this half-naked beauty next to him! Her name is Eris, and she has come to Earth to learn more about its inhabitants as a representative of the planet Catian. And she's decided to set up shop at Kio's home for her stay on Earth! Unbeknownst to Kio, there are quite a few organizations who will attempt to capture Eris, looking to keep her existence a secret by any means necessary. What's worse is when people around Kio turn out to secretly be a part of those organizations! Kio will have to work hard to keep Eris safe from these shady groups. Things are about to get mysterious, exciting, and most importantly sexy in Asobi ni Iku yo!

After a strategic maneuver, Senkuu Ishigami's team stalls Dr. Xeno's more scientifically advanced forces. A ceasefire between the two factions allows for the establishment of Corn City in North America, a hope for a future thriving population. Meanwhile, Senkuu and some of his teammates rush toward the Amazon in South America—the epicenter of the petrification beam's impact—to create Superalloy City and progress their spaceship project. With dangerous enemies still pursuing Senkuu and his companions, it is a race against time to reach the heart of the dense Amazon. As unexpected allies and scientific creations further fuel this leg of their journey, Senkuu is closer than ever to finally uncovering the mystery behind the petrification phenomenon.