DxD: The fake X fate - Chapter 19 -: Saji concurred

The story revolves around Charles Karino, a Levaamu Empire mercenary aerial pilot who mans the twin seater reconnaissance seaplane Santa Cruz. One day, he receives a preposterous assignment: to fly solo over 12,000 kilometers of enemy waters to protect a girl named Fana del Moral. Fana happens to be the next in line to the empire’s throne and a girl possessing beauty “equal to 5,000 beams of light.”

This is a standalone book. There’s another series under the name “To Aru Hikuushi e no Koiuta” (Love Song for a Certain Pilot) set in the same world, but in a completely different place and with different characters.

– Ulrezaj @ Mazui

Adapted to anime as “The Princess and the Pilot”

Tenjou Yuuya has been a bullied boy since the past.He lives in the home of his beloved grandfather while he goes to school. As usual, he receives a harsh bullying, and he takes an extended absence from school to have some time to heal his wounds.While on this long time of absence, he takes the opportunity to clean his grandfather’s house and goes to a room he never went before, where his grandfather keep many different objects that he gathered from his travels around the world. While he was arranging the objects, he found a door not on a wall among the objects.Out of curiosity he opens this door, what he found on the other side was…

Of the ancient gods only one remained in the world. This god lived alone for thousands of years and no longer had any desires. Legend had it that during the great war between the worlds he used his powers to turn the tide managing to seal the cataclysmic rift bringing order back into the three realms. Time flew by and hundreds of years passed in the blink of an eye.

In this time Shen Li was born into the demon world. Known as the Azure Sky King she was used to living a bright and dazzling life full of successes. Little did she know that her 1000th birthday would bring misfortune to her doorstep – a politically arranged marriage with her name on it. The Azure Sky King would henceforth marry the thirty-third grandson of the Heavenly Emperor, Fu Rongjun. This arranged marriage was meant to unite the Heavenly realm with the Demonic Realm, bringing the two together. Most would consider it good fortune to be related to the Emperor.

Unfortunately Fu Rongjun was infamous throughout the two realms for his Casanova personality. As the King who called the shots in the Demonic Realm, she had the ability to quell uprisings and end wars with a swing of her silver spear – there was absolutely no way she would marry such a flirtatious idiot. She had to escape from this marriage somehow even if it meant death!

In her escape Shen Li, never expected to meet a man that didn’t belong to any of the three realms. This oddball was truly strange!

- Description from Novelupdates