Erina Shindō (神堂 慧理那, Shindō Erina) is the tritagonist of Gonna be the Twin-Tail!!. Erina is the student council president of Yōgetsu High School. One day, when Soji first transformed into Tail Red, she was attacked by the Ultimagill the moment they appeared. Upon discovering Sōji and Aika were Tail Red and Tail Blue. She is known as Tail Yellow in her transformed state, and her weapon is Gun of Lightning, Vortex Blaster (雷の銃ヴォルテックスブラスター, Kaminari no Jū Vorutekkusu Burasutā).