Yuki Mita, a high school student with striking black hair and crimson eyes, harbors a complex history with Fukaya rooted in their childhood. Her relentless testing of substances and ideas on him forged a bond marred by distrust, driven by her fixation on crafting the ultimate aphrodisiac—a goal she pursues by targeting Fukaya as her primary test subject. This obsession underscores her manipulative, scheming persona.

Mita frequently disrupts Fukaya’s relationship with Fujino Shion through calculated interference. In one scheme, she hands Fujino a libido-enhancing potion while explicitly warning against its consumption. Ignoring the caution, Fujino drinks it, unleashing uncontrollable desires that force Fukaya to intervene. Later, Mita administers the same potion to Fukaya via a kiss, exploiting his heightened arousal to seduce him. She further complicates his life by capitalizing on his post-accident amnesia, falsely asserting herself as his girlfriend to deepen emotional entanglements.

Beneath her deceit lies an unreciprocated romantic yearning for Fukaya. When confronted after a compromising encounter, she dismisses her actions as playful teasing, yet her persistence in orchestrating elaborate ploys—such as bargaining with a teacher for a love potion by offering her own body—exposes unresolved attachment. Her demeanor shifts between cold manipulation and fleeting vulnerability, particularly when facing fallout from her schemes.

Across manga and OVA adaptations, Mita consistently antagonizes the central romance, deploying psychological tactics and pharmacological tricks to destabilize Fukaya’s bonds. Her arc emphasizes a ruthless pattern of experimentation, emotional exploitation, and ethical disregard, all cloaked beneath a carefully maintained guise of indifference.