I just listened to Toshl's "All Night Nippon". Toshl explained the meaning of his new nickname "龍玄とし(ryugentoshi)".
In the literal sense, 龍(ryu) means dragon.
玄(gen) means black, profound and turtle.
とし is hiragana of Toshi/Toshl.
"龍玄とし" is a combination of those 3 letters.
Toshl says he wants to rise like a dragon. At the same time, he wants to play beautiful music of an abyss step by step like a turtle. He says "Please remember my another name with these wishes"
Toshl's new song "Masquerade' was released as a name of "龍玄とし(ryugentoshi)".
Toshl didn't talk about this himself, but I found that 龍玄(ryugen) is also a name of Kamen Rider. Kamen Rider is a Japanese character wearing masks. (Kamen means mask in Japanese) Probably this nickname is related to his song title "Masquerade".
ㄴ It is written "龍玄とし" on the fan.
ㄴ This scarf pattern describes "龍玄".
You can see the hashtag #龍玄とし on his instagram.