Satou Kakeru has long accepted that his past life's memories of being a Hero in a fantasy world has no place in the current modern society. Until one day, the Demon King – Suzuki Teru – transfers into his school and throws Kakeru's normal life out of its axis.

An incident leads to their separation and three years later, Kakeru's big brother drops a bomb on him.

"They say the key to reviving the Demon King is in the academy island."

About the Title.

勇者だった俺は今世こそ平凡な人生を歩む! is the actual title of the story which can be roughly translated to "I, who was a hero, will walk an ordinary life in this world!"