R Position

Hydraulic pressure is applied to the servo valve to engage the reverse selector with the countershaft reverse gear and reverse selector hub while the shift lever is in the R position.
Hydraulic pressure is also applied to the 4th clutch, then the 4th clutch engages the mainshaft reverse gear with the mainshaft.
The mainshaft reverse gear drives the countershaft reverse gear via the reverse idler gear.
The rotational direction of the countershaft reverse gear is changed by the reverse idler gear.
The countershaft reverse gear drives the countershaft via the reverse selector, which drives the reverse selector hub.
Power is transmitted to the final drive gear, which in turn drives the final driven gear.

Fig 1: Identifying Power Flow R Position
Courtesy of AMERICAN HONDA MOTOR CO., INC.