Mikoto Saito is a high school student who attends the same school as Akina Myodo. Her status as a talented singer and beautiful idol makes her the focus of attention, despite receiving negative comments accusing her of being fake. She stars in advertisements and enjoys playing Cardfight!! Vanguard online before suddenly declaring a hiatus from her entertainment activities.

Her involvement with Vanguard began through online play via Cardfight!! Vanguard Dear Days, though she had no physical card game experience until being selected for the Fated Clash. She owns the Fated One of Ever-changing card and wields a Lyrical Monasterio deck featuring Fated One of Ever-changing, Krysrain as her ace unit. This deck strategy emphasizes playing cards with unique names to strengthen Krysrain and other units, leading her to include diverse Lyrical Monasterio cards in low quantities.

Mikoto learned of Akina Myodo's participation in the Fated Clash after witnessing his victory against Nao Inabe. Akina, sent by his sister Hikari Myodo, a Mikoto fan, brought her to meet Megumi Okura. Megumi helped Mikoto build her physical deck, and Mikoto won her first physical cardfight against Megumi. Her first official Fated Clash match pitted her against Taizo Kiyokura, whom she had met earlier during his hospital visit to Hikari alongside Akina. Taizo aggressively utilized his Product cards and defeated her.

Following the Fated Clash, Mikoto integrates into Akina's social circle. She begins spending time with Akina and Suo Yobitsugi, forming a trio that surprises classmates like Kento. This integration occurs after Akina's victory cured his sister Hikari, continuing into the period where Akina adjusts to Hikari's improved health and Suo displays increased happiness. She remains part of this group when they encounter new developments, such as the arrival of transfer student Kuon Aikawa.

Mikoto also has an insert song titled "Brand New!!" associated with her character.