The Legend of the Black Fallen Hero

Shin Denyuuden Kakumei-hen: Ochita Kuroi Yuusha no Densetsu
真伝勇伝・革命編 堕ちた黒い勇者の伝説

Source

Densetsu no Yūsha no Densetsu
Densetsu no Yuusha no Densetsu· 伝説の勇者の伝説
novel

Ryner Lute is a lazy student of the Roland Empire Royal Magician's Academy. One day, the Roland Empire goes to war against their neighboring country Estabul, and Ryner loses his classmates in the war. After the war, Ryner sets out on a journey to search for the relics of a "Legendary Hero" at King Sion Astal's command and finds out that a deadly curse is spreading throughout the continent.

Source

The Legend of the Black Fallen Hero
Ochita Kuroi Yuusha no Densetsu· 堕ちた黒い勇者の伝説
novel

Based on Sion Astal's points of view, this tells the story during Ryner's exile and how Sion fight against the King of Roland to gain the throne.

Source

The Legend of The Hero of Legend
Densetsu no Yuusha no Densetsu· 伝説の勇者の伝説
manga

A mythical story with swords and magic centering around one lethargic Roland Empire student named Ryner Lute. After getting dragged into a war and losing many of his friends, Ryner is asked by the soon-to-be enthroned king, Sion Astal, to help rebuild Roland postwar by searching for legendary relics. Accompanying him is a beautiful, capable, yet arrogant swordswoman named Ferris Eris, who’s always quick to insult and abuse Ryner. Meanwhile, a new turmoil begins to approach Roland.