Yoshiko Tsushima, who adopts the persona Yohane, attended Uranohoshi Girls' High School as a first-year before its closure and later Numazu High School. Born in Numazu City's urban area, she shares a kindergarten history with her friend Hanamaru Kunikida, whom she nicknames "Zuramaru." Her mother is a school teacher. Yoshiko's childhood fascination with "little devil" aesthetics evolved into the identity of "Yohane, the Fallen Angel," claiming she was cast from heaven for angering God. This persona became central to her self-expression in middle school, though it contributed to social difficulties and limited friendships during that time.

She exhibits traits of chuunibyou, characterized by grandiose delusions and her dramatic alter ego. As Yohane, she employs a lower-pitched voice, wears dark or devilish accessories, and refers to friends as "little demons." She insists on being called Yohane, rejecting her birth name and often crossing it out on introductions. Yoshiko perceives an extreme curse of bad luck, citing rain on trips, frequent falls in snow, consistent lottery losses, and illnesses before exams. She often blames herself for misfortunes affecting her group. Despite her flamboyant exterior, she struggles socially and feels embarrassed when her normal, higher-pitched voice surfaces, particularly when teased by friends like Hanamaru or Ruby Kurosawa.

Her personality contrasts sharply between her everyday self and her Yohane persona. When not roleplaying, she is sociable, sensitive to others' opinions, and self-aware about her eccentricities. Fear of ridicule over her Yohane behavior initially led her to avoid school. Her kindness manifests in actions like rescuing a dog with Riko Sakurauchi and helping Riko overcome a fear of dogs. She deeply treasures her friendships in Aqours for accepting her Yohane identity, especially with Hanamaru and Ruby. While relating more to indoor activities, she finds common ground with Mari Ohara during shared experiences, such as being forced indoors by rain.

Physically, Yoshiko has navy blue hair styled in a high bun on the right side and pink eyes. Her design incorporates midnight blue, symbolizing the night sky and heaven, and purple eyes, representing a blend of her reserved nature and Yohane's intensity. She frequently wears black-and-white clothing, reflecting her identity's duality.

Her hobbies and skills include playing video games, favoring fighting and racing genres, performing magic tricks, video editing for Aqours, and live-streaming fortune-telling sessions online. She enjoys spicy foods like takoyaki with Tabasco sauce, chocolate, and strawberries, but dislikes oranges and coffee.

Her development shows gradual self-acceptance. During Aqours' formation, she initially left after her "fallen angel" theme caused issues with the student council president but rejoined when members affirmed their acceptance of her persona. This reinforced her decision to retain the Yohane identity as an intrinsic part of herself, symbolizing a rejection of ordinary existence. She influences her subunit Guilty Kiss, contributing to its thematic and musical direction.

Relationships within Aqours highlight her growth. She shares a longstanding bond with Hanamaru, who often coaxes her out of Yohane-related antics. Her dynamic with Riko involves mutual support, exemplified by the dog-rescue incident. She also connects with Mari over shared indoor preferences during group activities. These interactions underscore her integration despite initial social hesitations.