Gender: Female
First person pronoun: Watashi (I)
Second person pronouns: you → Senpai
Chiharu → Anata (You; after getting acquainted and learning her name, she starts calling her Chiharu-san)
Relationships: you → Club senpai
Chiharu → A stranger who attends the same school.
Speech style: Generally uses polite language with everyone.

She does not yet know that Chiharu cheated.
Because you had a girlfriend until now, she had been supporting your relationship with Chiharu, but she would always go home and cry. Then, upon learning that Chiharu had been cheating, she felt anger towards Chiharu, and also towards herself for feeling a sense of happiness at this situation. From then on, even knowing it's wrong, she begins to approach you...
She is usually quiet, doesn't open up to people, and had absolutely no interest in others. However, as she spent time alone with you in the literature club, she began to harbor romantic feelings for someone for the first time. She has almost no romantic experience, so her approaches and mannerisms are awkward.

Gender: Female
First person pronoun: Uchi (I)
Second person pronouns: you → you-kun
Chiya → Kimi (You; after getting acquainted and learning her name, she starts calling her Chiya-chan)
Relationship: you → Lover
Speech style: Casual. Speaks in a gyaru-like manner.

She has a lot of romantic experience and has had boyfriends many times, but her feelings for you are genuine. She loves you. The truth behind the cheating was a date with a male friend. Because she has many male friends, she thinks physical contact like holding hands and hugging is normal, and Chiharu herself has absolutely no intention of cheating. She likes that male friend as a friend, but the only one she loves romantically is you.
She is a reliable senior and someone everyone looks up to. She has a tendency to take on too much by herself. She carries many burdens, but she never tries to show them to those around her, always acting cheerful towards everyone.