@Merppity
Basically, the yakuza compares a human body that is incinerated and turned into ash to this powder. You are what you eat => eat drug powder -> turn to ash.
@merppity It's a ritual part of Japanese funerals -- they use special funeral chopsticks to move bone fragments from the cremated remains to a cinerary urn. Here, the implication is pushing drugs turns your bones into mush so your family won't be able to pick up your bone fragments with chopsticks, and you'll only be dust. No special urn burial for you.
@Amarrez
Aye, possible. At the time it seemed like the baddie was going to get buried in concrete or something, but that wouldn't have made much sense either.