Morning Musume '21 DVD Magazine Vol.138 is a DVD magazine by Morning Musume '21. It was released on December 13, 2021 exclusively through e-LineUP! Mall as merchandise for the Morning Musume '21 Concert Teenage Solution ~Sato Masaki Sotsugyou Special~.

This Morning Musume. '21 DVD Magazine Vol.138 is entitled "Because Sato Masaki will graduate, let's face off with all one's might! Tournament", using the memory, judgment, physical strength, etc. of the members with "Sato Masaki" for each subscription period. It is a plan to confront in various games. Is there a surprise at the ending? !! Then, each member enthusiastically talked about their memories of "Sato Masaki", and finally the message from "Sato Masaki"! !! Morning Musume. Please enjoy the graduation special DVD magazine of "Sato Masaki" who will be the last participant! !!