Shizuku Minase lives as the stoic older brother to Minase Arisa after their parents' disappearance, sharing a home yet rarely initiating conversation or revealing emotion through expression. His reserved exterior masks profound care for his sister, demonstrated through gifts and gestures aimed at easing her loneliness—a bond forged by their shared parental absence.

Within Wonderland, he transforms into the Black Rabbit, a guide tasked with leading Arisa into this realm. Here, he vehemently rejects his identity as Shizuku, denies all familial ties, and operates within Wonderland's cyclical time loop, creating a stark contrast to his real-world self.

This protective devotion manifests violently during crises. When confronting the character Shadow, he annihilates Wonderland itself to save Arisa from immediate peril, sacrificing all other inhabitants without hesitation. However, rejection from Arisa—particularly in narratives involving rivals like Nao Kurotani (Cheshire Cat)—unravels his stability. He spirals into self-destruction, attempting suicide in certain Wonderland conclusions. In the "School Garden" arc, his refusal to accept Arisa's happiness with others escalates to eliminating romantic rivals, resulting in a murder-suicide in one bad ending or a cataclysmic rage that kills him and collapses Wonderland in another.

Physically, Shizuku has black hair and central heterochromia blending brown and red in his eyes. He typically wears a school uniform with glasses and a coat. As the Black Rabbit, he retains these traits while incorporating rabbit-themed elements into his appearance.

His entire existence pivots on the conflict between possessive, all-consuming loyalty to Arisa and the detached obligations of his Wonderland role—a tension driving his actions whenever their bond is threatened or she rejects him.