Gonna Be the Twin-Tail!!

Original title: 俺、ツインテールになります。

Souji Mitsuka is a first-year high school student who is obsessed with twin-tails. One day, a beautiful girl from a parallel world named Twoearle, suddenly appeared in front of him and gave him the power to transform into the twin-tailed warrior Tail Red. With the Ultimegil organization attacking the planet, Souji now must fight in order to protect the peace on Earth.