Giyuu has a sleeper build. And everyone has found out about that one time when they were training together. They rarely saw the man training because he's sleeping. He's very introverted, and he rarely socialise so anything normal he does would be a surprise to everyone. They decided that every once in a month, they'll do an arm wrestle contest. Giyuu was forced to participate because he's hashira. He had won a lot. One time he was so sleepy, that he fell asleep while arm wrestling with Sanemi. He thought it'd be in easy win but no, Giyuu's instincts despite being asleep, kept his grip strong and firm. The man was stronger while sleeping. Damn. This shocked everyone, they've never seen someone who's stronger while sleeping than awake. Sanemi was PISSED, he can't believe this emotionless dude can beat him. While sleeping only tho. So he beat everyone but Gyomei because- that's understandable. It's Gyomei.

It kept happening during contests. And Giyuu had no idea about his secret talent because he was asleep.