The Goth-Loli Sisters are four girls who are completely obsessed with the main boys of the series.
Initially their roles in the storyline were much smaller, but were expanded within the anime to provide comic relief. They usually have a cameo appearance in each episode saying their catch phrase "Goth-Goth, Loli-Loli" while crossing their own fingers.
Their first appearance in the manga was a one shot of them getting revenge on Sunako Nakahara and Noi Kasahara for being so close to the men they love. A notable aspect to their characters is that instead of actively pursuing their crushes, they instead sat in the background and waited for them to notice them instead. In the manga they were responsible for a number of disturbances, such as replacing the boys' lunches with their (rather horrible) home-made lunches.
Their attempts to get closer to their respective crushes culminated in them attempting to harm Noi for her close relationship to Takanaga and the others. This attempt was foiled after they were discovered by a rage-driven Sunako, only to be spared by the boys' arrival in restraining Sunako.
They make a reappearance when they enlist Sunako's help in talking with the boys by bribing her with four extremely rare skeleton dolls. Each girl eventually chickens out of her respective encounter, becoming overwhelmed by the aura of the boys which ruin the respective romantic fantasies each goth-loli girl has. The fantasies come to a disturbing conclusion when each girl replaces the hero with an image of Sunako, who they've come to admire.
Their appearance is an exaggeration of the Gothic Lolita phenomenon, and are very unattractive. Their names are given as Ierie, Machapi, Maririn and Mintan in the Singaporean English-language translation.