Arifureta Shokugyou de Sekai Saikyou (WN) - Chapter 509

10 years searching for his lost sibling.

A demon phoenix cultivator died in the hands of his beloved and was merged with a young master with the same name. Their souls were fused and now, the new Feng Fei Yun is struggling to become stronger and survive in the human world.

What do you do when your brother dies because of some entitled assholes? You go undercover.My real name? Clare. But at school, I’m Clause—just another guy blending in. Disguised. Watching. Yes, a boy. No, it's not an all-boys school—I'm just deep undercover, hunting down the bastard responsible for my brother’s suicide. Nobody—and I mean nobody—messes with my precious brother and gets away with it. They better pray I never find them, because when I do? Death will be a mercy, and trust me—I don’t do mercy.And as for the egotistical Alpha and the narcissistic Vampire Prince? They can go fuck themselves. I don’t do mates, I don’t do claiming, and I sure as hell don’t do them.

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.