R Position

Hydraulic pressure is applied to the servo valve to engage the reverse selector with the countershaft (reverse gear while the shift lever is in R position).
Hydraulic pressure is also applied to the 5th clutch, then the 5th clutch engages the mainshaft reverse gear with the mainshaft.
The mainshaft reverse gear drives the countershaft reverse gear via the reverse idler gear.
The rotation direction of the countershaft reverse gear is changed via 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: Automatic Transmission In R Position

Courtesy of AMERICAN HONDA MOTOR CO., INC.