Kōrin Tatsunagi emerges as a key player across interconnected narratives, first appearing within Team Ultra-Rare alongside sisters Rekka and Suiko—later clarified in certain timelines as non-biological allies. She co-manages the PSY card shop and spearheads the Miyaji Academy Cardfight Club’s creation, enforcing strict entry by challenging prospects to defeat her in combat. Her poised, disciplined daily demeanor contrasts with a flashy idol persona during public engagements, a duality destabilized by her vulnerability to external psychological manipulation.

Under such influence, her personality fractures into a cold, possessive alter ego fixated on dominating Aichi Sendou through psychological reversal—a stark departure from her innate loyalty. This core drive compels her to absorb destructive energies to protect others, often endangering herself. Her bond with Aichi evolves from wariness to profound emotional stakes, marked by transferring her avatar card to him, intercepting threats to his safety, and prioritizing his well-being over personal consequences.

Combat mirrors her shifting allegiances: she wields Royal Paladin, Angel Feather, and Link Joker clan decks across arcs, adopting aggressive reversed-state tactics via units like Broken Heart Jewel Knight, Ashlei "Яeverse." External forces repeatedly rewrite her past, erasing her from others’ memories—yet fragments linger, as seen in Misaki Tokura retaining a gifted hairband or allies sensing unexplained absences. Alternate timelines cast her as a "Called Walker" under Takuto Tatsunagi’s control, her identity suppressed until bonds with Aichi and the Cardfight Club reignite her defiance. These arcs culminate in her rejecting manipulation to safeguard those connections.

Her legacy persists through honorary club memberships post-timeline resets, faint imprints on allies’ choices, and symbolic gestures that echo her impact even when her presence fades from recorded history.