From MoonFlower Scans:

Mustuki Yoneya, a high schooler, feels insecure and jealous because her constant companion and best friend, Nishio Kyuteki is starting to pay attention to a beautiful upperclassman. Seeing the senpai's attractiveness as a threat to her wish to remain at her best friend's side forever, she tries out several attempts as she strives to become the main object of Kyuteki's attention.

Note: Original language image is not available.