A Breakthrough Came Out by Forbidden Master and Disciple.

禁断師弟でブレイクスルー ~勇者の息子が魔王の弟子で何が悪い~

Kindan Shitei de Breakthrough: Yuusha no Musuko ga Maou no Deshi de Nani ga Warui

20 chapters

2 volumes

2019 – 2020

The hero's son and the ghost of the Demon King become master and pupil. Eirth, son of the hero who vanquished the Great Demon King, struggles under constant pressure. No matter how hard he tries or what results he achieves, it is never enough for those around him. He hears "I'm a disappointment compared to my father" and "Don't you know you're the son of the hero!" every day. Living like this, Eirth encounters his fate in the room that holds his father the hero's sword. "Interesting. I will train you. I have only free time now." To get back at his parents and the world, Eirth receives special personal training from the Demon King. In the days that follow, his parents, the heroes of the past, his first love—the princess childhood friend—the geniuses of the era, and the world itself will tremble before him.