First-year high schooler Souji Mitsuka spends his free time rating classmates' twintail hairstyles and running a one-member fan club dedicated to them. When the alien invaders Ultimegil attack Earth to harvest humanity's spiritual energy, the extraterrestrial Twoearle recruits him to fight back by transforming into the twin-tailed warrior Tail Red. Alongside fellow fighters Aika Tsube and Erina Shindou, Souji turns his hairstyle obsession into humanity's last line of defense.