BTOB's Yook Sungjae shares an episode about his fluent Japanese... ”When BTOB wasn't popular”

BTOB's Yook Sungjae revealed the secret to his Japanese language skills.
Korea" posted a video titled "Yook Sungjae is in his prime every day. When do you think you look good even when you look at yourself?"
In this video, in response to the question, "What is the secret to your good Japanese?", Sungjae began by saying, "Back when BTOB wasn't really popular..."
Sungjae explained, "There was a time when I worked really hard during my activities in Japan, and I think that's when the words started to come out naturally."
He also added, "I like singing Japanese songs."