Oh no... I am having bad vibes from the art and the start of the story. Not saying that the art is bad, but I've seen media of this sort that didn't appeal to me. Like it's a generic story that is too fast and no build up. Hope I am wrong tho
The moment lots of men are surrounding a girl, even if they are not in love, they call it a harem xDdd But yes, I understand harem tag as men in love with the female lead
Because in the main casts (the main group protags) there is only one girl (Yona) and many men. So even though there is no romance with them (except for one, Hak and Yona) it's still a genre of the manga.
It's a wonderful and sad story.