2500 years ago, in India, Siddhartha was born as a prince of the Shakya clan, but he gives up his position as a prince to see the world. While he travels he meets a strange boy named Assaji, who can predict the future and a monk with only one eye. Overwhelmed by the sufferings he witnesses around him, Siddhartha strives to restore peace. Meanwhile, Prince Ruri of Kosara begins his attack on the Shakya clan. (Source: IMDB)

When ordinary high school student Aoba Watase is suddenly targeted by a giant robot known as a Valiancer, he is saved by his mysterious classmate Hina Yumihara. After revealing that she and their robotic enemy are from the future, Hina suddenly propels Aoba 70 years forward in order to prevent his death. Upon arrival, Aoba finds himself in the cockpit of a Valiancer called Luxon, stuck in the midst of a firefight between the military forces of the Free Pact Alliance (FPA) and Zogilia Republic. After he shows high compatibility with an FPA pilot named Dio Weinberg, the two perform a successful coupling, allowing them to share experiences and subsequently increase their capabilities and skills. Although Aoba is able to survive this unexpected battle, he is taken into custody by the FPA ship Cygnus, who wishes to interrogate him. While the student's main concern is whether he will ever be able to return home, what he doesn't realize is that he is about to get caught up in a war to protect the world.

Neo Kyoto is a place where everything is decided through the card game Build Divide. From resolving personal conflicts to determining social status, success in Build Divide means success in life. The biggest ambition of every player is to become the King, whose peerless skills grant them near-total rule over the city. One day, a young man wakes up in Neo Kyoto—with the knowledge of just his name, Teruto Kurabe, and carrying only a deck for a card game he no longer knows. Teruto soon encounters another player, Sakura Banka, who helps him remember both how to play Build Divide and his original mission: that no matter what, he must meet the King. Teaming up together, Teruto and Sakura find that their best chance for a royal audience is with the Rebuild tournament, where the one who collects twenty-one tokens from other competitors can challenge the King for their throne. However, as Teruto continues to play, he begins to regain his lost memories that call into question the very nature of Neo Kyoto.

Following a ruthless attack from an imperialist criminal gang known as the Masked Demons, Shinsengumi's Eighth Division—the law-enforcing squad in Kyoto that remains faithful to the shogunate—is nearly annihilated, with its sole survivor, Heisuke Toudou, critically injured. Urged to rebuild the Shinsengumi by the local feudal lord, Katamori Matsudaira, Toudou decides to offer eight convicts the chance to redeem themselves: they must abandon their old names and become substitutes for the eight Shinsengumi captains. All accept but one, who ends up immediately executed by the former assassin Sakuya. However, Toudou has a hard time transforming the seven reformed criminals into loyal servants. Due to his lack of discipline, the impulsive and vengeful Ichibanboshi, whose family perished at the hands of the Masked Demons, threatens the success of Toudou's strategy. As Toudou pledges to protect the shogunate against imperialists and foreign invaders, other factions, such as Kogorou Katsura's group, start to put their plans in motion with only one goal in mind—to seize power at the dusk of the Edo period.