Suiko Tatsunagi stands as the eldest sister to Rekka and Kourin Tatsunagi. She co-manages the card shop PSY and performs with the idol group Team Ultra-Rare. Her involvement begins by facilitating crucial events, notably providing Aichi Sendou with the King of Knights, Alfred card. She observes events with calm reserve. Her abilities allow her to perceive happenings on the planets Cray and Brandt, establishing her as a bridge between dimensions. During the first season, she actively triggers PSY Qualia abilities in pivotal characters. She is heavily implied to have instigated Ren Suzugamori's initial descent into using this power, fracturing his friendship with Kai and Tetsu. Later, she presents both Ren and Aichi with critical choices between cards representing light and darkness, shaping their paths. When Aichi hesitates, the cards merge into Majesty Lord Blaster, which she deems suitable. Her motivations remain ambiguous, prioritizing clashes of ideals among her chosen fighters over personal transparency, even towards her sisters. In the second season, she travels internationally with Team Ultra-Rare as part of the VF Circuit entertainment. During this phase, she adopts an Angel Feather deck centered on Chief Nurse, Shamsiel and the Pegasus series, emphasizing defensive playstyles leveraging damage zone mechanics. This deck aligns with her idol group's thematic motif rather than her historical preferences. Her involvement intensifies in the third season when she enrolls at Fukuhara High School under Takuto Tatsunagi's direction. There, she develops a rivalry with Naoki Ishida after he criticizes her sailor uniform; she retaliates by defeating him in a cardfight using precise defensive tactics. During high school tournament qualifiers, she faces Naoki again, acknowledging his growth despite her loss. Subsequently, she is corrupted by the Link Joker entity, switching to a Gravity Dragon-centered deck. In this reversed state, she battles Ren Suzugamori but loses when he activates Raging Form Dragon. The manga continuity reveals her indirect influence through a flashback, confirming her role in catalyzing Ren's initial embrace of PSY Qualia during his youth, permanently altering his relationships. In the V Series reboot, she appears as a tertiary antagonist under mind control as a PSYqualia Zombie. Forced into this state, she infects others like Minami Kawanami and Asaka Narumi while spying on Ren. After Kouji Ibuki frees her, her connection to Vanguard severs, leaving her emotionally detached yet still aligned with Takuto Tatsunagi's objectives. This incarnation is later erased from collective memory as a Called Walker. The "IF" spin-off storyline depicts an alternate version where she partners with Kouji Ibuki to rectify distorted realities. In this narrative, she supports the Blaster Pair (Emi Sendou and Shuka) by manifesting units like Wingal Brave through "Realize" summoning. Her commitment to correcting timeline anomalies remains central, though she operates without her original memories or powers. Her surname combines the characters for "standing" (立) and "calm" (凪), reflecting her poised disposition.