THE STRONGEST KNIGHTESS CANNOT ESCAPE AN OBSESSIVE PRINCE!

The Strongest Knightess Cannot Escape An Obsessive Prince! summary:

Mila, a member of the king's personal guard, has unrequited feelings for her liege, King Alec.
However, due to a certain incident, she ends up becoming the object of obsession to his younger brother, Prince Elge, a man she does not like at all. She desperately tries to keep her distance from him, avoiding him like the plague, but one day, she is assigned to accompany Prince Elge for a tour surveying the kingdom. During that tour Mila attempts to escape at night, but the prince will not have it. He mercilessly takes her virginity, and from then on sexually assails her day and day again. This is the story of one such unlucky knightess.

There is a TL and R18 version.