It began in 1945, at the end of the Pacific War. Alien invaders filled the earth's Skies, and mankind was forced to confront an unprecedented threat. For the first time in human history, people of all cultures came together under one banner. 
This war has now been raging for over fifty years. Countless lives have been lost, and the Japanese military is now forced to rely on young people such as Atsushi Hayami and his high school class, also known as Unit 5121. This new generation fearlessly struggles on with the aid of the HWT humanoid combat machines and the devastating PBE bomb. 
(Source: Media Blasters)

In 1945, at the close of the Pacific War, an invasion beset the planet Earth. Droves of Phantom Beasts - aliens from another world - landed and waged war against man. Humanity was forced to unite and fight this common threat, but years later, in present times, the death toll has depleted the military forces, leaving Japan with no choice: They must enlist the help of teenagers. Atsushi Hayami is among those who, rather than lead a normal high-school life, must take up arms to ensure the survival of mankind. 
 
(Source: ADV)

An anthology of short stories with such creators as: Shizuru Hayashiya (Onegai Teacher), Kuroyuri Hime (Aquarian Age) and Yuna Takanagi (Fire Emblem Thracia 776). 
Credit - Anime News Network

Motoko Hara