Boys und Panzer, basically. When cold war up to modern tanks/vehicles enter Sensha-dō (or tankery), but falls under a separate league, and is only exclusive for boys. And with that, begins the story and journey of a transferee student named Ryota, who suddenly ends up joining Sensha-dō despite trying to avoid it. (Disclaimer: I do not own the GuP franchise in any way. Along with the references I made/will make throughout the storyline.)

The Empress of man had created 20 Primarchs to be her generals and leaders during the great crusade. Each one had there own unique and special abilities. However something went wrong and a extra primarch was born, the man YN LN would lead the 21st Legion against the horrors of the galaxy. Can he bound with his fellow warlords and unite the galaxy, or will he watch it burn?