MTL - In Different World with Naruto System - Chapter 325 Bauxite reincarnation

I returned to Earth as the invincible Knight King. But the Gods came with me.

After dying from a strange terminal illness, Ling Lan was reborn into a world 10,000 years into the future. Although she dearly wished she could just live a peaceful and uneventful life in her new healthy body, fate had other plans…

Forced to disguise herself as a boy just so she could inherit her deceased father’s premium military benefits, Ling Lan’s journey to adulthood was full of challenges. After much difficulty, she finally turned sixteen when she could drop the charade. But before she could grasp her newfound freedom to get married and start her own family, a twist of fate results in her being thrown into the Federation’s top military boys’ school.

With these twists of fate, Ling Lan had little choice but to walk further and further down a path of no return, one of cold and aloof dominance…

- Description from Novelupdates

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.