Well the answer is out of convenience. I wasnt really attached to my characters name when i first started playing the game in 2016 I just came up with whatever, so by the time I was deep in it after shb launch in 2019 I kinda didnt want to refer to my wol by name, and also I wanted to keep her name private so people couldnt find me in game. And I had played in jp up until shb so it just felt appropriate to say wolchan. just "wol" felt a little to formal for her. No deeper reason than that