Emi Sendō serves as Aichi Sendō's younger sister. In the original timeline, she exhibits a caring and mature nature, protectively ensuring Aichi prepares for school and returns punctually. Her curiosity about the Vanguard card game sparks after noticing its positive effect on Aichi's confidence. She learns the game by borrowing an Oracle Think Tank deck before constructing her own Bermuda Triangle deck, specializing in powerful yet adorable units like Riviere and Pacifica. Displaying natural talent, she triumphs in junior tournaments and continues competing across events.

Within the distorted reality of *Cardfight!! Vanguard Extra Story -IF-*, where Vanguard vanishes and Aichi disappears, Emi emerges as the protagonist. She transforms into a magical girl, partnering with the card fairy Shuka to form the "Blaster Pair." Together they combat the entity Jammer to restore the true timeline. Emi dons a magical girl outfit accented in white, blue, and a pink ribbon. After history’s restoration, she adapts this attire as casual wear and temporarily wears Aichi’s light blue jacket during her journey.

Driven by her mission to locate Aichi in the *-IF-* world, Emi allies with Kouji Ibuki—transplanted from the original timeline—and the inadvertently involved Suiko Tatsunagi. Using magical abilities to summon Vanguard units in battle, they confront Jammer’s forces to recover the true history and return Aichi. Following the timeline’s restoration, Emi retains aspects of her magical girl identity. She joins Shuka in a stage play, announcing "Blaster Pair" for an upcoming show. During a cardfight in the restored world, she wields Aichi’s Royal Paladin deck against Toshiki Kai and secures victory.