Nanako Kuroi (黒井 ななこ, Kuroi Nanako) is the homeroom teacher for Konata Izumi's class and her primary subject is world history. She is more like a friend than their teacher, as she has a lax personality. Consequently, she frequently borrows and exchanges video games with Konata, and is in Konata's guild in the same online game, where she plays as a wizard. Still single, she is constantly online, even on Christmas and New Year's Eve. Nanako has very long, blonde hair, which she ties at the back of her neck, and her eyes are green. She also has a sharp tooth protruding from one corner of her mouth. When writing on the chalkboard, Nanako is able to become ambidextrous. She loves to watch baseball, and is a big fan of the Chiba Lotte Marines. Also, Nanako speaks in a fake Kansai accent. A running gag within the series is whenever Konata and Nanako are both online together, Nanako tells her to stop slacking off. She is also completely oblivious to Yui Narumi's marital status, often using Yui as a source of understanding regarding the life of being single.