Gonna be the Twin-Tail!! (tv-series, 2014)

Mitsuka Souji is a first year high school student who greatly loves twintails. One day, a beautiful girl named Thuearle, who comes from another world, suddenly appeared in front of him and gave him the power to transform into the twintails warrior Tail Red. Now Souji must fight in order to protect the peace on Earth with the help of his childhood friend Tsube Aika, who can become the twintails warrior Tail Blue, all while keeping the twintails warriors' real identities hidden and dealing with the fact that Tail Red is actually female