It was 1969.
Strange "living vehicles" appeared out of nowhere and started conquering nations.
Overwhelmed, the people fought back, but we lost out.

Jipang, the "land of the arousing daughter", had few resources
but was succeeded in creating a system where a single person could withstand
huge amounts of firepower. There was one caveat:

The system was perversely limited to use by young girls.

Two candidates were inducted into the system and unleashed on the enemy.

* YOU must press on!
Deal epic destruction as a bullet-spraying missile-launching
Japanese girl against overwhelming oddness, revel in the destruction
in the alternate warscape of future-past 1969!
press onward into enemy territory dealing swaths of glorious destruction!

* And of COURSE (?)..
Should you fail there's assault animations to behold!
Trample into battle with an eye for "winning" AND "losing"
utilizing the Sex Streak System:

- Chain your attacks to produce a massive super-explosion!
- Get assaulted for a sustained length and power up!

Turn the tables from violation to victory. That's the Sex Stream System's merit!

[From DLsite English]