Wakatsuki Tsukasa

"I... don't want to lose anything else. I don't want to lose her... Don't make me live life alone. Save me... Save me, Tomo Nii-san..."

- Wakatsuki Tsukasa, It's my Own Invention

A childhood friend of Minakami Yuki, and a gentle, kind girl who's loved by everyone. Despite being the younger twin of Wakatsuki Kagami, she has the composure of an older sister. They're incredibly close, like they're two halves of one whole.

Part of an existence that has been torn in half. Depending on the perspective, she represents someone to be hated, or someone to be protected.

Appearance
Tsukasa has medium length violet hair she ties into a small and messy side ponytail with a gold-black ribbon and violet eyes. She also wears two yellow hair pins. She's always seen wearing the Kita High uniform except for one instance in Down the Rabbit Hole I, when she wore a beige button up dress as nightwear.

Personality
Tsukasa has a calm, mature and gentle personality, often feeling like an older sister more than the little sister. She often plays the role of mediator between Yuki and Kagami. She cares about her sister deeply, as she tries to encourage Kagami to confess her feelings to Yuki repeatedly despite harboring feelings for Yuki herself. She's a part of the school's disciplinary committee and a huge fan of the Romance of the Three Kingdoms.

Tsukasa is a representation of Hasaki in the same way Kagami is a representation of Hasaki's rabbit doll. Mamiya Takuji sees Hasaki as Tsukasa in order to maintain internal consistency regarding his imagined narrative that Hasaki is dead, and forces the Yuki of the Down the Rabbit Hole I & II chapters to see her that way as well.

Plot
Tsukasa is a projection of Hasaki developed by Takuji after the birth of his personality. He creates Tsukasa and by extension Kagami to keep the internal logic of his world consistent with his delusion that Hasaki is dead.

Tsukasa also appears in the dream world of Rabbit Hole I alongside Yuki, Kagami and Zakuro.

Her last chronological appearance is to Yuki in Takuji's underground base, where Yuki once again sees Hasaki as Tsukasa. After the second Minakami Yuki and Mamiya Takuji's personalities die, Tsukasa and Kagami's forms disappear forever.

Wakatsuki Kagami
Wakatsuki Kagami is Tsukasa's twin sister. Kagami is very protective of Tsukasa and never lets anyone get away with insulting her or making fun of her, even Yuki. Though Kagami is the older twin, Tsukasa's maturity makes her seem like the older one instead.

Minakami Yuki
Minakami Yuki is a childhood friend of Tsukasa. She seemingly has feelings for Yuki, but still tries to set Yuki up with Kagami. She often plays mediator between Kagami and Yuki.

Mamiya Takuji
The creator of Tsukasa's form. Despite being her creator, he hates Kagami and Tsukasa, likely because they are a symbol of his younger twin sister Hasaki, who he despises. He eventually loses his cool and makes Tsukasa watch as Kagami is raped and crucified by his followers.

Trivia

 * Tsukasa is based on the Lucky Star character, Hiiragi Tsukasa.