Owari no Chronicle - Volume 14, Afterword

After choking to death on a watermelon, Rong Jiahui thought that she would enter the netherworld and be reincarnated.

But when she opened her eyes, she discovered, to her very horror, that she had returned twelve years into the past…

Looking at the beautiful and awkward “little brother” that would be conferred the title of Marshal in the future for outstanding military service, she almost let out a snort of laughter.

She firmly decided to hug the thigh of this little brother, and climb to the top of her life!

The plan was beautiful, but it had just one problem.

Why had this little brother… suddenly turned into…

A little sister…

- Description from Novelupdates

Levian's life was supposed to be over.His awakening at the ceremony had failed seven times, and he had been left without powers. A man without powers was useless in war and a disgrace to their family.However, Levian's luck was greater than he could ever imagine.That same night, he found an awakening stone on his bed. One that looked different from any other he had seen before.Levian did not hesitate to try an eighth time.[Legendary Weapons Talent, awakened!][Weapon Fusion Talent, Awakened!][Mythical Weapon Potential!]With this, his life changes for the better.However, his awakening brings about other troubles and secrets that he had no clue of.Ones that threaten not only him, but the entire world itself.[THE ENTITIES ARE COMING!]Follow Levian on his journey towards legendary weapons mastery.

What the hell? That menace who bullied me since I was six years old, actually became a pretty girl after three years of living apart? And she even ran to our agreed duel location to confess to me, hoping that I can become her boyfriend?!

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