King Gwanggaeto is like Alexander of Macedonia. He drastically expanded the Goguryeo's territory during his rein. However, episodes dealing with his westward expansion toward China, and battle against Japanese troops who invaded Silla were dropped from the story.
Still it is not enough for China, I guess. To me, Guardian is more like Goguryeo Yonga(or Sonata) where suave royal prince weaves many love affairs with female deities or real girls in acient Goguryeo.
I have to question why it has to be King Gwanggaeto to make the drama work. I know it is the most attention-drawing choice, but Gwanggaeto is not known as a love prince in any known accounts of history. He was rather quite busy running the state and waging a war.
I’d ban that Mr. Lady too ;-)