Modern day Japan.
Earthlings make first contact with an unknown alien species from Mars.
The Martians have begun an invasion of the planet.
It begins by getting close to Earth's most powerful officials and
impregnating them with tentacles, making them allies.
A hentai takeover, not a hostile one; no blood spilled, but so much semen!
The Martians are thriving among us! We're just GIVING it away!

Meet protagonist Tako Rice.
A hero who embraces the call of duty with open arms...
not! He's a naughty hentai space alien who loves interspecies sex.
Tako Rice is shirking his invasion duties to have loads
of sex however he pleases! Because it's fun!

[From DLsite English]