Zuruko Sasuga, alias Tigerlily Sakai in international adaptations, serves as Yuna’s cousin and a pivotal force within their relationship. Introduced as Yuna’s new instructor, she maintains a polished public persona defined by athletic prowess, naginata mastery, and a flair for stylish attire. Behind this facade lies a manipulative cunning and self-serving tendencies, earning the moniker “Zuru-ko” from Yuna for her sly exploitation of others’ vulnerabilities.

Her dynamic with Yuna is volatile, oscillating between coercion and retaliation. Zuruko weaponizes threats—such as exposing Yuna’s academic struggles to their grandmother—to enforce obedience, framing her harsh tactics as a self-appointed role as a disciplinarian. Yet beneath their clashes simmers an undercurrent of mutual loyalty, with Zuruko sporadically shielding Yuna from harm, even as she twists such acts to reinforce control.

Relocating to Okinawa New Town following her school’s shutdown triggers a nuanced evolution in Zuruko’s demeanor. Though her authoritarian streak endures, subtle softened edges emerge, particularly in her uncharacteristic affection for Stitch, contrasting her typically brusque demeanor. She shares Yuna’s dread of thunderstorms, a vulnerability Yuna occasionally turns against her in mischievous payback.

Romantically pursued by Koji, Taka, Masa, and Mr. Honda, Zuruko balances these attentions with enduring friendships dating to junior high, notably with Takumi’s twin sisters Mitsuki and Hazuki. While her abrasive exterior dominates, fleeting yet sincere gestures toward Yuna offer glimpses of a layered psyche beneath her strategic exterior.