Gonna be the Twin-Tail!!

, abbreviated , is a Japanese light novel series written by Yume Mizusawa and illustrated by Ayumu Kasuga. Shogakukan has published nineteen volumes under their Gagaga Bunko imprint since June 2012. An anime adaptation produced by Production IMS aired in Japan from October 9, 2014 to December 25, 2014.
Plot.
Soji Mitsuka is an ordinary high school boy who has an obsession for twintail hair. One day he encounters a mysterious girl named Twoearle, who is from a parallel world, when monsters appear in his town and declare that all twintails in the world belong to them. These monsters feed off "attribute strength", the spiritual energy of humans. Twoearle entrusted Soji with Tail Gear, imaginary armor initiated by powerful twintail attributes. With the armor, Soji transforms into a girl and branded Tail Red, to protect Earth.
Characters.
Ultimegil.
 is an organization of phantom-monsters called Eremerian that traverse different worlds, seeking a variety of "attributes". Although they are the villains of the story, the majority of them are rather silly and comical and behave much like otakus, often admiring cute girls, collecting dolls, and even adoring the twintail heroines. Having discovered Earth is rich in "attributes", they began to colonize and make plans to conquer the Earth. Members include:
Media.
Light novels.
"Ore, Twintail ni Narimasu." began as a light novel series written by Yume Mizusawa, with illustrations by Ayumu Kasuga. Mizusawa originally entered the first novel in the series, originally titled , into Shogakukan's sixth Shogakukan Light Novel Prize in 2011 and the novel won the judge's prize. The first novel was published by Shogakukan on June 19, 2012 under their Gagaga Bunko imprint, and fourteen novels have been released as of December 19, 2017.
The series was originally slated to conclude in October 2018, with the release of its 16th volume. However, a 17th volume was released on March 19, 2019.
Manga.
A manga adaptation titled by Ryōta Suzuki was serialized in Square Enix's "Monthly Big Gangan" magazine, and was compiled into two tankōbon volumes.
Anime.
An anime television series adaptation, produced by Production IMS and directed by Hiroyuki , aired in Japan from October 9, 2014 to December 25, 2014. The opening theme is by Maaya Uchida. The ending theme is sung by the voice actresses of the three main heroines: Tail Red (Sumire Uesaka), Tail Blue (Yūka Aisaka), and Tail Yellow (Chinatsu Akasaki). Both singles for the opening and ending themes were released on October 22, 2014. The anime has been licensed for streaming in North America by Funimation and in the Middle East, North Africa, Europe (excluding UK and Scandinavia) by Crunchyroll and AnimeLab in Australia and New Zealand.