Tetsuya - The Man Called Mahjong Master - Vol. 11 Ch. 86 - Paper Tiger

[MangaDex]

 

[Doomroar]

Honestly surprised it took them this long to figure out it was his glasses

 

[ThatGuy]

Tetsu is so cool!

 

[BlackMage]

Honestly surprised it took them this long to figure out it was his glasses

Tetsu figures it out in 2 chapters (3 if you count this one for the explanation) or 40 minutes IRL. I don't think it's that long.