The BBC News article Hayabusa-2: Japanese probe set to 'bomb' an asteroid says:
The charge is carried on the Small Carry-On Impactor (SCI) device.
This is a 14kg conical container attached to Hayabusa-2 and packed with plastic explosive.
The SCI is due to separate from Hayabusa-2 at 01:56 GMT on Friday at an altitude of 500m above the surface of Ryugu. That will kick off a 40-minute countdown to detonation. When the device explodes, it is expected to punch a 10m-wide hole in the asteroid.
In the meantime, Hayabusa-2 should have manoeuvred itself to hide away on the other side of the asteroid, shielding the spacecraft from any flying debris.
The answer to How far will the debris cloud from Hayabusa-2's touch-and-go sample recovery travel around Ryugu? Will any have escaped to heliocentric orbit? makes it clear that even low-velocity projectiles produced near Ryugu's surface could travel in Ryugu-centric as well as heliocentric orbits. Of course since the Ryugu-centric (elliptical) orbits intersect the surface at one point, they'll intersect somewhere else as well, and either come gently to rest or scatter secondary additional projectiles.
So just because Hayabusa-2 will move to the other side doesn't mean it can't get hit by something.
I'm curious what kinds of debris Hayabusa-2 mission-planners at JAXA might have thought about, so I'd like to ask: How far will Hayabusa-2 back off before the "bomb" goes off?