Every kingdom must always be wary of its enemies and never let its guard down. This was a lesson Eldior’s father failed to learn: the prince was caught off guard by an invasion of his kingdom, forcing his father to help him flee as quickly as possible to seek aid from an allied nation. The way he managed to go unnoticed was by dressing as a woman: after all, they were looking for a prince. During his escape, he ends up receiving help from a group of warriors through a favorable agreement.
During their journey, they uncover the motivations behind the invasion of Eldior’s kingdom — there is more to it than just the plundering of treasures and lands. The group faces an enemy much closer than they imagine, with grave consequences.
(Source: Mythos, translated)
— Description from AniList community (anilist.co).