In the bustling and futuristic city of Heartland, a young boy named Yuuma Tsukumo has a dream that everyone his age wants to achieve—earning the title of the greatest duelist! Sadly, due to his lackluster dueling skills, this dream is far from achievable. But when the school bully, Ryouga "Shark" Kamishiro, splits the key given to him by his father into two pieces, he inadvertently sets Yuuma on a collision course with his dream. Retaining one half of the key, Yuuma begins a duel with Shark, but soon realizes that his inexperienced skills are no match for him. In a sudden turn of events, Yuuma's key repairs itself, and the "Door of Destiny'' appears before him. Using the key to open it, Yuuma is greeted by an alien by the name of Astral—a being only he can see. The bewildered Yuuma soon learns that his memories have been divided into 100 "Number Cards," all of which he must retrieve. However, he is also not the only one looking for them. Bombarded by these revelations, Yuuma, alongside Astral, must defend the world from the upcoming threats that loom over Heartland City—regardless of any divine intervention that may occur.

Within the horse-racing world, the horse girls of Team Spica have been gaining popularity as they continue to rack up victories. The one receiving the most attention in the group is Toukai Teiou, known for her cheerful personality and exceptional running skills. Teiou aims to become an undefeated Triple Crown horse girl by winning all three G1 races consecutively, a feat that has not been accomplished since the legendary Symbolic Rudolf managed to do so many years ago. On her path to obtaining the Triple Crown, Teiou is met with many challenges, encountering both old and new rivals. Amidst her fierce rivalries, however, Teiou is soon confronted with decisions that will leave a huge impact on her very own racing career. [Written by MAL Rewrite]

In its expansion west to gain resources, the Europan Imperial Alliance invades the neutral Principality of Gallia, seeking to take control of its vast Ragnite deposits. Their strategic advantage, technological superiority, and military might make opposition nonexistent, so they steamroll through the border of the sleepy principality with ease. As Imperial forces run through his quiet hometown, Welkin Gunther and his younger sister Isara jump into action, banding with the leader of the local militia to push the occupational forces out of the village. Quickly retreating to the Gallian capital, they are organized into a unit with the remnants of the militia, tasked with assisting in repelling the Imperial presence from the country. Though unfamiliar with war, the newly formed Squad Seven must defend their country from annexation. But as the battle rages on through the streets of Gallia, ancient secrets will bring the team closer than they'd ever anticipated.

In the lead-up to a photoshoot in which Yua Nakabeni and Ren Aikawa have been invited to model for an illustrator, the two girls are feeling anxious. To help them out, their friend and fellow classmate Homi Moegi decides to run a practice shoot in hopes of easing their nerves. Yua and Ren repeatedly tense up during shots on their own, so Homi asks them to pair up for some couple shots, hoping that they will relax in each other's company. What begins as a series of cute poses soon turns into an alluring collage of legs encased in black stockings layered over one another.