Mimic demon king becomes a teacher

A mimic, who managed to become a demon king, has reigned for over a millenia, but now he has become old. To combat his age, he goes to deep sleep in order to regain his former vitality.
Low and behold, he spends more time sleeping than he had immagined, and now the world has changed from what he knew. In trying to find if any of his old friends survived, he ends up becoming a teacher in prestigious academy.

During his teaching career, he finds out that the one person he truly loved still exist. His secret wife on his secret life. Turns out his life is centered around helping his wife in her grand plan. He might be, what cultured people call, a SIMP for his wife to the point of wanting to kill anyone who ridicules her.

After working as a teacher for a while to a quite talent filled class, he finally sees his wife and soon after, the grand plan will be finalized and all will become clear to this once great mimic.