Unofficial biography, made by me. Contains lots of spoilers for the series. I will make a spoiler-free Chihaya Kisaragi biography soon.

Name: Chihaya Kisaragi
Real name: Chihara Kisaragi (如月 千原)
Age: 16
Eye Color: Brown
Location: Kyoto (originally from Hyogo Prefecture)
Personality: Cold, lonely, stoic, yet polite.
Voice Actor: Chihaya Suzuki
Debut Episode: Season 1, Episode 3
Nicknames: Chihaya (universal nickname), Kisaragi (by the school), Chiha (by Matsu), Haya-san (by Azusa), idolmaster (by Takane)
Current status: Dead
Name Meaning: Chihaya is a mixture of the kanji for thousand (sen / 千) and early (haya / 早). Her real last name has the kanji for original (hara / 原). Kisaragi is a mixture of the kanji for alike (如) and moon / month (tsuki / 月).

Chihaya Kisaragi is a 16 year old girl who often runs away from school, due to her family situation. After her little brother died, her parents fought a lot, and her mother took her with her to Kyoto. She wants to grow up to be a classical singer. She is very antisocial, and would rather listen to her music than listen to her school stuff. Despite this, she is actually a kind and polite soul. She eventually learns of Takane's existence, and due to that, Chihaya started idolizing her; in fact, she even calls her "Graceful Takane." In return, Takane calls her an idolmaster due to Chihaya idolizing her a lot.

Chihaya becomes an amateur scientist in Season 2. However, it comes with some costs. In season 2, episode 5, Chihaya Kisaragi gets severely ill from a science experiment gone wrong, and her life ended shortly afterwards. She requested for Takane Shijou to be at her side during her last moments of life, before Chihaya finally passed away. Unfortunately, Takane was stuck in traffic, and it was already too late; Chihaya was gone when Takane arrived. Takane was devastated at the loss of her idolmaster and then showed an emotional moment.

Although Chihaya is currently dead, she makes an appearance in some of Takane's flashbacks, and appears in the intro of the third season of the series.

Facts
She has blue hair like Azusa Miura; she kind of has something for Azusa.
While her name, Chihara, comes from Chihara Minori, a singer, her nickname, Chihaya, is taken from the name of her voice actor.
She shares her nickname with Chihaya Ayase, from Chihayafuru. She is compared to Tsumugi Shiraishi from the Million Live; however, unlike Tsumugi, she is more cold and stoic, while Tsumugi is more sharp-tongued.
She loves to get tans at the beach.
She wanted to major in science, if she did go to college.
She never dated; she thinks that love is silly.
She has a beautiful singing voice; if you were to hear it, you would be inspired.
Her original name was Minako Sakikawa (咲川 美菜子).