I haven't found a chapter to summarize yet, so I'm considering a different world——
Identity is Killua's younger brother, white hair. (Since he doesn't want to inherit the family business, don't force it)
The content shouldn't expand too much about the Dark Continent. After all, it's not like the old thief can hand over a manuscript.
Concept: Due to the unreliability of the brothers, a history of blood and tears of fighting for the family business at a young age