Clan Building System: I'm not the Protagonist?! - Chapter 1 - 30th Birthday Celebration.

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

Trying to hit on Shinobu mommy.

A young Brave walked out of his village, gathered companions to his side, defeated the Great Demon King, became famous, then came back with beauties in hand! This was a legend that appears in the world of Seyrol every 200 years!

Our protagonist, however, isn’t a Brave. Even so, for over a thousand years his figure has loomed throughout its history.

Unwittingly, the name of the Red-robed Priest began to resound throughout the world. Red-robed Priest’s legend included extraordinary sword techniques and magic, erudite knowledge, and an almost prophetic ability to lead young Braves toward the proper path. People of the world think of him as a descendent of the ancient Yellow Race which led to his omnipotence. In essence, however, this was just the characteristics of the profession known as ‘Noble’.

- Description from Novelupdates

Kai of the Sorcerer’s Tower is one of the last mages left, barely surviving in a world ruled by creatures of the dark — where the era of mages ended, and most of the lands got contaminated with dead mana. To save his world and fulfil his master’s last wish, he put himself through a forbidden ritual, risking his soul being ripped into pieces to make his way into the past. In an era with abundant mana — an era yet to enter the Golden Era of Magic. Things go wrong, of course, as they always do, and he finds himself thousands of years before the world fell to mana contamination — in the body of a young lord, Arzan. All is not well, though, as the young lord was murdered by someone right at the cusp of a beast wave threatening the territory, while larger threats loom on the horizon. There was a lot to do for Kai to regain his former strength in this time of primitive technology, but then again, he might just be able to change that.