What I learnt about them today from pixiv (it might fanon since I don’t know much about them as canon):
1. 鬼白 is spelled as Onishiro as word. And HooHaku as their name abbreviation.
2. Hoozuki called Hakutaku as シロブタ = White pig because Shiro taken from his name, and buta taken from playboy Chinese Journey To The West Cho Hakkai who is half human and pig.
3. Hakutaku can put a soul to his drawing (mostly represented by his fugly cat drawing) with lifespan for 3 days.
And Hoozuki’s obsession to goldfish was because it resembled Hakutaku’s clothes in his god version WWWWWWWWWWWWWW.
4. Hoozuki and Hakutaku might know each other from the beginning because a lot of fans made child!Hoozuki had Hakutaku as his guardian (??).
5. They might care for each other long time ago, but having eternal life might mess around with their memories. Perhaps they are hardly remember what they used to be.
6. Hoozuki might a sadist, but he is pretty tsundere and hid his feeling very well through violence and become yandere while Hakutaku always holding back when Hoozuki hurt him because if he snapped, he might hurt Hoozuki pretty bad wwwwwwwwwww
PS. Most of them were information I gather through pixiv since we don’t have much english chapter. Do not trust me they are my headcanon anyway www.
If anyone could provide canon information about due from the JP/CH manga, please share them with me because I need them for making doujinshi about them sob soob.