When he was younger, Daisuke Toujima and his friends were involved in an incident that changed their lives forever. Now in high school, Daisuke is always ready for the worst, preparing his body and mind for anything. One day while they were at school, Daisuke, his friends, and the rest of their classmates were transported 300 years into the future. The future world they find themselves in i filled with nothing but rundown buildings and deadly mechanical monsters called "Revisions." With the help of a woman named Milo, Daisuke and his friends Gai, Ru, Marimari, and Keisaku fight against the monsters as they search for a way to return home.

Egao no Daika tells the story of two Kingdoms who are on the brink of war. Harlant is a bustling nation where everyone is able to prosper. However, the same can not be said for the neighboring country of Grandiga, who seeks to take control of Harlant's land. Despite the impending war, Yuki, the princess of Harlant, has continued to live a happy live alongside her bodyguard Joshua. Unfortunately for Yuki, her happy days soon come to an end as she learns about the war and what it means for her people.