Hi Emma,

Yes, you can use the HVL-F28RM wirelessly with the ILCE-7RM5 through Radio Control Wireless Flash or Wireless Radio Receiver like the FA-WRR1 (sold separately.
You can configure either of the following devices as the commander unit, and then use the commander unit to trigger the flash operation of this flash unit that is not attached to a camera and is configured as the receiver unit.
Another flash unit that is attached to the camera and supports radio wireless communications
a radio wireless commander that is attached to the camera
Commander unit
This flash unit (HVL-F28RM) configured as the receiver unit
For the commander unit, you can use this flash unit or a radio wireless commander.

Work with the menu of the camera attached with this flash unit to specify [On] for [Wireless Flash].
For details on the settings of the camera, refer to the operating instructions supplied with your camera.

Turn the power switch on the flash unit to “A,” “B,” or “C.”
The flash unit is configured as a member of a wireless group (“A,” “B,” or “C”).

Attach the mini-stand to the flash unit.
Attach another flash unit of the same model (HVL-F28RM) that is configured as the commander unit, or a radio wireless commander to the camera.
When using another flash unit of the same model (HVL-F28RM), make sure that its power switch is turned to “ON.”

Place the camera and this flash unit.
Make sure that the flash unit attached to the camera (the commander unit) and this flash unit (the receiver unit) are wirelessly connected and ready to fire.
When wirelessly connected:

The LINK lamp is lit in green.

When ready to fire:

The TEST button is lit in orange.

Press the shutter button on the camera to take a photo.
To fire test flashes, press the TEST button on the commander unit.

Sony Europe BV.

I don't know if this flash works with alpha 7 R V!