Galko's very tall classmate who has a bad posture due to her height, and is also interested in the occult. The boys start stalking her after they learn from Galko that she also has big breasts.

The anime follows the everyday lives of three high school girls who are close friends: Galko, Otako, and Ojou. Galko is a slightly foul-mouthed but good-natured girl who is popular in her class. Her hobby is film appreciation. Otako is a girl who sits in the corner of the classroom, but for some reason is good friends with Galko. Ojou is an airheaded girl who often talks with Galko and Otako. 
 
Each of the girls' names refers to their type. Galko is a pun on gyaru or gal, which is a term used to describe a type of street fashion where women in their teens and 20s bleach their hair and wear highly decorated nails and a lot of makeup. Otako is a pun on otaku, and Ojou refers to a girl who is a daughter of a high-class family. 
 
(Source: Anime News Network)

Galko-chan always speaks her mind, which may not be the wisest decision in all cases, but it’s never short of entertaining! Follow the exuberant and unbelievably busty high schooler as she traverses the ups and downs of adolescence with spirit and verve, alongside her best friends–the anti-social loner, Otako, and the unpredictably honest Ojou.
 (Source: Seven Seas Entertainment)
 
Notes: 
- Includes 9 extras chapters from the volume release. 
- Serialization of this series was suspended on December 24, 2021 following the mangaka's arrest.

Oshiete! Galko-chan OVA bundled w/ LE manga vol.4

Okako