I think the setting is a game-like world where the protagonist becomes a demon lord (or something similar) and his friends become heroes.
The main character has to hide his identity from his classmates. One of his (female) teachers is his subordinate in the isekai.
Sounds like Ecstas Online.
The story centers on Kakeru Doumeguri, a loner who is at the lowest caste of his school. A certain incident makes him reincarnate as the Dark Lord Helschaft, who exists inside the virtual reality game "Exodia Exodus," though he also has the ability to turn back into human form.
Ririko Asagiri, a girl who Kakeru has long had a crush on, is also trapped in the game, along with her classmates, who all swear a vow to defeat Helschaft and get back to their world. However, if Helschaft dies, everyone's lives will be in danger, so Kakeru/Helschaft meets them in battle. The other characters include Shuuko Aikawa, Kakeru's boss at his part-time job in the real world, and Helschaft's slave in the game; and Non Shizukuishi, a sharp-tongued cool girl who is interested in Helschaft.
The MC is a high school student, who also works part time as the developer of a Japanese role-playing video game, featuring a Demon King as the main villain. One day, he and his classmates are transported into the world of this video game, with him as the Demon King, and them as the heroes.
It turns out that his boss at the company he worked for has also been transported into the game world as one of his subordinates. She informs him that he must keep his identity as the Demon King a secret from his classmates, since there's an item that could kill him if they learn the truth.
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