Here comes the official source
nobody had answered the question so far, so here it goes:
JAPAN AIP ENR 3.5
3.9 Strategic Lateral Offsets Procedures in Fukuoka FIR
3.9.1 This procedure is to be used for both wake vortex encounters, and to mitigate the heightened risk of collision when non-normal events such as operational altitude deviation errors and turbulence induced altitude deviations occur.
3.9.2 Offsets are only applied in the oceanic control area over the Pacific Ocean within the Fukuoka FIR.
3.9.3 Offsets are applied only by aircraft with automatic offset tracking capability.
3.9.4 The following requirements apply to the use of the offset:
(1) The decision to apply a strategic lateral offset is the responsibility of the flight crew.
(2) The offset shall be established at a distance in tenths of a nautical mile up to a maximum of 2NM to the right of the center line relative to the direction of flight.
(3) The strategic lateral offset procedure has been designed to include offsets to mitigate the effects of wake turbulence of preceding aircraft.
(4) There is no ATC clearance required for this procedure and, above it is not necessary that ATC be advised.
(5) Voice position reports are to be based on the current ATC route/course clearance and not the exact coordinates of the offset position.
(6) When radar identification is established, pilots shall fly on the centerline.