A gate to another dimension has burst open, and from it emerge gigantic invincible creatures that threaten all of humanity. Earth's only defense is a mysterious group of warriors who have co-opted the alien technology in order to fight back!

The border defense organization "Border" was established to fight against the attacks of the "Neighbors" who possess unknown power. Osamu Mikumo, a member of the Border, forms the Mikumo Squad with Yuma Kuga, a Neighbor who he met by chance, and his childhood friend Chika Ametori, and they struggle to win the internal Border rankings in order to join the expeditionary force to the Neighborhood.

With Hyuse joining the Tamakoma Squad, the rank wars are continuing and the Tamakoma squad are striving to get selected for the Away Missions.