As an Ogre, Hakurou was a short old man, contrary to the general Ogre physique, with aged silver hair and two white, ivory-like horns protruding from his forehead. His hair was gently wavy and has two bangs dropping from the far side of his horns, and a ponytail tied with a string. He also had pointed ears and has black eye lines on his lower eyelids. Similar to the other Ogres, in the Anime, his skin had a very subtle silver tint to go with his color scheme - a tint so subtle that it's only noticeable if compared to his Kijin form side by side.
His attire consisted of an off white robe with thick black outlines, fastened by a pale brown ribbon on his waist. This whole was also covered another similar robe which was kept unfastened. Finally, he wore a thick pale brown scarf that always covered his mouth, a pair of loose white pants, wooden sandals, black fingerless gloves that attached only to his middle finger over the back of his hands, and a plane looking thin Japanese sword.
Similar to all evolutions, Hakurou is going from a shabby (but sharp) old man to middle-aged man in his prime. Rimuru described his a 'romance gray', as someone who has perhaps had many adventures in the past and is stick kicking to go, which is what 'man's romance' is.
His hair was more full and became sharper (less droopy) and his skin lost the silver tint. His horns shrunk a lot, and perhaps the biggest change he had was his facial structure going from a stubby to one having really sharp and well-defined jaws and chin. Moreover, unknown if he had one in his Ogre stage, he got a long silver goatee (short in the Manga).
His new attire consisted of a white overcoat, which turn was covered on the shoulders and neck by some kind of overwear as well. In the Manga and Light Novel, however, he wore a scarf.
No notable visual changes compared to Hakurou's Kijin stage.
Hakurou is usually calm. Although he's at the age to be someone's grandpa, his spirit is clearly years younger.
Hakurou is the descendant of the master swordsman Araki Byakuya.
Hakurou was the Ogre Tribe's martial instructor and the strongest swordsman of their royal guard.
He is also the one that trained Gazel Dwargo in his swordsmanship 200 years ago.
Despite Ogres only having an average lifespan of about 100 years, Hakurou miraculously managed to live for about 300 years as an Ogre, before meeting Rimuru and extending his lifespan through evolution into a Kijin.