|Kanji Name||八坂 こう|
|Romaji Name||Yasaka Kō|
|Date of Birth||February 3|
|Seiyū||Rika Morinaga (Ryoo Gakuen Otosai)|
|Manga Debut||Manga Episode 117|
Kō Yasaka (八坂 こう, Yasaka Kō) is the president of the Animation Research Club, and is also the treasurer of the Student Council. She is called "Kō-chan-senpai" (こーちゃん先輩, "Kō-chan-senpai"?) by her juniors, including Hiyori, who is a member of the Animation Research Club.
She is studying at Ryōō High School in class 2-F and is the only second year among the Lucky Star girls at the time of her appearance (the rest being either first or third year students and soon her class friends Miku and Tamaki were introduced). She enjoys playing anime-themed fighting games, and also likes to check on new and trendy things, never failing to miss one. She has played fighting games with Konata before (always losing to Konata, so much that Konata has gotten bored of her), and does not notice that Konata is her senior(but she soon noticed her in school). She has tanned skin, and likes dōjinshi, manga, observing people, chatting, and gambling. In Lucky Star: Ryōō Gakuen Ōtōsai, she is a good friend of Yamato Nagamori.
- Hiyori Tamura
- Yutaka Kobayakawa
- Minami Iwasaki
- Konata Izumi
- Patricia Martin
- Kagami Hiiragi
- Tsukasa Hiiragi
- Miyuki Takara
- Tamaki Yamanobe
- Miku Busujima
- Izumi Wakase
- Ko is one of the tallest characters, having the same height as Miyuki and Patricia which is 168cm.
- She is so far the second character to have somewhat tomboyish personality(the first being Misao).
|Konata Izumi - Tsukasa Hiiragi - Miyuki Takara - Kagami Hiiragi - Ayano Minegishi - Misao Kusakabe - Yutaka Kobayakawa - Minami Iwasaki - Hiyori Tamura - Patricia Martin|
|Sōjirō Izumi - Kanata Izumi - Yui Narumi - Tadao Hiiragi - Miki Hiiragi - Matsuri Hiiragi - Inori Hiiragi - Yukari Takara - Honoka Iwasaki - Nanako Kuroi - Hikaru Sakuraba - Hinata Miyakawa - Hikage Miyakawa - Akira Kogami|
|Goldy - Cherry|
|Anime Only Characters|
|Minoru Shiraishi - Meito Anizawa - Daisuke Ono - Gotouza|
|Manga Only Characters|
|Kō Yasaka - Yamato Nagamori - Izumi Wakase - Fuyuki Amahara - Tamaki Yamanobe - Miku Busujima|