[1] Mandy Sekiguchi was born on January 25, 1991, in New Jersey, United States and grew up in Shinagawa, Tokyo.

Mandy advanced into acting for the first time in April 2014, when he was selected as a cast member of Fuji TV's late night program Wow.

On June 5, 2018, he threw the first pitch at the opening ceremony of the Giants vs Rakuten baseball game, held at Tokyo Dome.

[2] His appearance garnered great public attention since the speed of his pitch reached 133 km/h, the fastest thrown by an entertainer at that time.

[17][18] On March 18, Mandy was invited to throw another first pitch at the opening ceremony of the Giants vs Mariners baseball game at Tokyo Dome.

It included "Control Myself" as a B-side track, being the group's first original English song and also the first one to feature Mandy as a rapper.

[23] On January 25, 2025, Sekiguchi announced his marriage to a non-celebrity woman through a post on his official social media account.