Mashiro is a Japanese manga artist best known as the creator of the romantic comedy series My Love Story With Yamada-kun at Lv999. Mashiro’s interest in creating manga began in childhood, influenced by their mother, who had also aimed to become a manga artist, allowing Mashiro to grow up surrounded by manga manuscripts. This early exposure directly inspired their career path.

Mashiro is the sole writer and illustrator of My Love Story With Yamada-kun at Lv999. The series started serialization on Comic Smart's Ganma! manga website on March 7, 2019. The story follows a college student and an elite gamer, and Mashiro has stated that a personal love of video games was a primary reason for choosing to center the manga around gaming culture. The manga has been collected into multiple print volumes by Media Factory under their MF Comics imprint, and an English print release has been distributed by Penguin Random House's Inklore imprint. The series achieved significant commercial success, with over one million copies sold in Japan.

The work was adapted into an anime television series produced by the studio Madhouse, which aired from April to June 2023. Mashiro was involved in the anime's production, participating in scenario meetings, casting decisions, recording sessions, and the supervision of images. The creator has expressed surprise and happiness at the series receiving an anime adaptation. As of October 2023, the individual chapters of the manga had been collected into eight tankōbon volumes.