Silent Witch - Chapter Volume 9 5: The Hero’s Substitute

From a media tycoon’s daughter to a poor plumber’s girl, but it seems that Yu Yao is unfazed? She opened the eyes of the sky, and her life has been opened all the way. She is an eighteen-year-old girl, but as soon as she turns around, she becomes a big boss who no one in the entertainment industry dares to offend.

- Description from Novelupdates

In the age of the Great Liang Dynasty, the lives of the people were made convenient with steam-powered machines that run on a fuel named Violetstream Gold. Chang Geng, who lived in a small countryside village, shared a distant relationship with his mother while his stepfather was away most of the year round, and the only people he was close to were two little kids, the village teacher, and his yi fu – adoptive father. But his life was flipped upside down one day following the barbaric Man tribes’ invasion, and it turned out that his entire identity had been an illusion – not only was Chang Geng himself not the country boy he thought he was, but also his mother, his teacher, and even his beloved yi fu…

As monstrous invaders ravage the world, Ryzen Kael— a man shattered by a tragedy ten years ago— faces his final moments. But just as death closes in, a mysterious system awakens within him, offering a path beyond his limits.Now, with nothing left to lose, he steps into a dangerous journey of survival and power, defying fate and unlocking abilities beyond imagination. Follow his rise as he challenges destiny itself, carving his name into history!Author's other storiesThe Unrivaled Holder: Rise of the Dragon Monarch - 3rd Season Ongoing

Long Fei, a cross-timer and doujin, is an otaku who traveled to another world. In the original world, he was an otaku fan of Gundam and military science fiction.

He died in an accident and was reincarnated into another world. The Gundam works he had read before his death and the techniques in various military novels could be brought to another world.

How would he use the Gundam that Long Fei created? What waves can be caused in this different world?