Hakutaku is a Celestial Beast and pharmacist living in Togenkyo at the Sentou Farm in Heaven. He took in Momotaro as his assistant and has been imparting his skills to the ex-ogre slayer ever since. He dwells among rabbits who also learn medical skills from him and aid him in preparation of herbal concoctions. Hoozuki is his arch-nemesis despite their many similarities.
Hakutaku comes across as gracious and charming and is extremely popular with the ladies, much as Hoozuki is. However he is an unrepentant womanizer and flirts with every pretty woman he sees including Peach Maki and Oko. It is this quality that both Hoozuki and Momotaro find extremely distasteful about Hakutaku though they seem to have accepted it with time.
Hakutaku claims that his popularity with women stems from the fact that his medical skills are much admired by womenfolk. This seems accurate as most of his callers are female asking him for herbal remedies. Unfortunately, his philandering ways also tends to enrage the women he is two-timing, leading to him being dumped as often as he gains a new girlfriend.
(Source: Hoozuki no Reitetsu Wikia)