Make your char array 7 bytes:
storage[7];
then send just like this (just tested and works):
Blynk.virtualWrite(Vx, storage);
You need the last byte to be blank (NULL actually, which it is by default after you declare it) then virtualWrite treats it as a String.
Edit: BTW the data will be no use at all on the Blynk app but it is a way of storing the data in a virtual pin for use later, after reset etc.