Clan Immortal Cultivation: I Can See Hints - Chapter 1056 - 650: Starlight Ancient Spear (Seeking Subscriptions and Monthly Votes)

This story is centered around the man named Yi Ji-Hyuk, who has spent 1000 years in a Medieval Western fantasy-like world before returning back to the modern-day Earth. When he returns, he finds that his home is facing monster threats, and that humans with superpowers have appeared to protect the innocent people of Earth.

Seventeen-year-old Hajime Nagumo is your average, everyday otaku. However, his simple life of pulling all-nighters and sleeping in school is suddenly turned upside down when he, along with the rest of his class, is summoned to a fantasy world!

In a time when the Divine Prefectures of the East Sea were in great disarray, Emperor Ye Qing and Donghuang the Great appeared to save the day. Under their rule, the prefectures united and all nations as well as their kings have been controlled. However, the legend of these two great heroes becomes altered when Emperor Ye Qing’s name is wiped from the history books after his sudden death. All statues and images of him were destroyed and his name a taboo. Only the legend of Donghuang the Great shall live on.

Fifteen years later, a young man by the name of Ye Futian begins his journey in search for his true identity. The legend of Futian was going to be one for the history books.

- Description from Novelupdates

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?

- Description from novelbuddy