Castle of Black Iron - Chapter 1938 - Descension

Crossing to One Piece world, he became Roger’s younger brother.

Young Chen Xiang had a fateful encounter with a goddess & demoness and received their peerless heritage, divine pulses, ultimate martial arts, and transcendent alchemy techniques, which gave him an easy ride in his journey of cultivation.

Chen Shiping, a Qi training monk from the Foundation Establishment family, is struggling in the world of cultivating immortals

- Description from novelbuddy

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”