It takes place in 1969 in an alternative universe/timeline where Japan is infiltrated by mysterious invaders called the, err... mysterious "Invaders". Earth Defense Organization AEGIS has a secret weapon against the naughty Invaders, which happens to be a schoolgirl named Izuniko Ikusawa, who can open a door to another dimension and draw devastating supernatural powers from there. This volume contains episodes 19 thru 21.