The Desolate Era (Web Novel) - Book 42, Chapter 21 - Glad You Are Safe

As a precocious child, Lycoris suffers from a strange sense of deja vu. On the day her father told her about her fiancé, she realizes that her fiancé was a character from an otome game she once played in a previous life.

He became a teacher at the best magic academy in the empire.
….For being mistaken for someone else.

Reincarnated as the eldest son of Ming Taizu Zhu Yuanzhang, the biological father of Emperor Jianwen, and the elder brother of Ming Chengzu Zhu Di.

See how Yiwen Prince Zhu Biao, who was fleeting like a meteor in history, survived the turbulent Hongwu years and built a new Ming Dynasty!

(No system, no plug-ins, no IQ crushing, no cross-age technology tree)

- Description from novelbuddy

The one single goal in life of the Strongest Old Sage is to subjugate the Demon King. In an epic final battle, both of them met their mutual destruction at each other’s hands.

However, the Demon King was not completely destroyed!

In order to destroy the Demon King once and for all; post-death, the Old Sage trains in the World of Gods and reincarnates as the Apostle of the Gods, Will.

In the reincarnated future, the Old Sage had become a legend and his former disciples hold the supreme authority in the world. The disciples had created an organization to oppose the Demon King and an academy to nurture the new generation of Heroes.

Thus the Apostle of the Gods, Will (8 year old), enrols into that Academy of Heroes.

This is the story of a boy on a mission to save the world through epic battles while enjoying Academy life.