The author seems to have two nicknames: Izumo and White Sunny.
Izumo may most likely be his middle name. White Sunny seems to be an actual nickname that was extended from his original first name "Sun." "White" may just indicate his brightness/intelligence or something of that nature.
It was also rumored that he sometimes wears a "WHITE" Chinese mask on his face when he draws his art. The reason why is still a mystery.