Hello , I will tell everyone about how Ahri can hear Sona.
When I talked on LoL Wiki chatroom , I found my new friend "Mineko Charat Lucky".
I asked him to find why Ahri could hear Sona, and he gave this information.
Kitsunes, or Gumihos grow an extra tail every one hundred years. It takes eight hundred years for a gumiho to have nine tails.
Obviously, to live even one hundred years, lots of physical and mental training is mandatory. During this long period of training, gumihos develop an ability to talk to spirits and souls out of boredom training alone.
Eventually, they will gain the ability to speak to humans through their minds without talking.
Now, because Ahri is a Gumiho, she can speak through this method.
This explains why Ahri can hear and talk with Sona like she does with spirits and souls.
Some information links :
And this picture is drawn by me.
Please share it if you like the concept.
I hope Riot will know this.