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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 Tamura, who is a member of the Animation Research Club. In Lucky Star: Ryōō Gakuen Ōtōsai, she is a good friend of Yamato Nagamori.


Kō is introduced as a second-year student at Ryōō High School. 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 Izumi 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). Conversely, Konata never notices Kō until after graduation.

In volume 7, Kō begins her third year and notices a love letter left on her desk before class one day. After finding out that it was not addressed to her, she passes the letter to Hiyori Tamura, who passes it to Tsukasa Hiiragi, who in turn passes it to Kagami Hiiragi, the addressee. Kagami later finds out that Konata had written the letter and snuck it under her desk before graduation, and word of this returns to Kō.

Kō finally interacts with Konata in Nostalgic Place (chapter 199), who had returned to Ryōō High disguised as a student.




  • 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).