Emi Sendō, the younger sister of Aichi Sendō, attends Miyaji Academy as an elementary student, embodying a caring, mature demeanor that often shifts into a motherly role. She diligently ensures her brother wakes on time, returns home promptly, and finishes homework, driven by concern for his timid nature and history of bullying. Witnessing his growing confidence through the card game Vanguard, she investigates its impact, visiting Card Capital to observe his matches and recognize his evolution into a more assertive self. Initially disinterested in playing, she later learns Vanguard under Shin Nitta and Morikawa’s tutelage. Early strategies prioritize aesthetics, favoring "cute" cards and avoiding Lozenge Magus’s sacrifice. Gradually honing her skills, she defeats Morikawa in her debut and claims victory in a shop tournament’s Junior Division using a Bermuda Triangle clan deck featuring Riviere and Pacifica. Her deck evolves across seasons, integrating PR♥ISM units and Twinkle Happiness☆, Pacifica, reflecting her tactical growth. Beyond personal play, she supports Team Q4 during tournaments, aids Misaki Tokura in confronting her past through a cardfight, and joins team training sessions. By Season 3, she co-establishes Miyaji Middle School’s Vanguard Cardfight Circle, showcasing leadership by defeating rival Shingo Komoi. In Season 4, her memories of Aichi vanish after his disappearance, leaving her puzzled when questioned about him, yet she continues playing Vanguard alongside Mai Tobita. The *-IF-* spin-off presents an alternate reality where Aichi’s absence leads Emi to ally with fairy Shuka as the magical girl duo Blaster Pair, battling antagonist Jammer to restore the original timeline. Adopting a white-and-blue magical persona, she later blends elements of this attire into her everyday style post-restoration. In a pivotal clash against Toshiki Kai, she wields Aichi’s Royal Paladin deck, symbolizing their enduring bond. Her dynamic with Kamui Katsuragi involves his unspoken, unreciprocated affection, which she remains oblivious to. The surname Sendō, meaning "leadership" or "guidance," mirrors her narrative role as a supportive figure. Notably, she emerges as the franchise’s first female protagonist in a season, cementing her expanded-media significance.