Sunao Cool Princess Sayaka to Nangoku Oukyuu Kozukuri ~Nuicha Yada... Aka-chan Dekiru made Shikyuu ni Dashite Hoshii~

The main character is an ordinary student.
One day, he is kidnapped by someone and when he wakes up, he finds himself surrounded by 3 beautiful women in a luxury palace.
They turn out to be princesses in a small tropical country and ask for the childmaking to be regarded as the official couple.

[From English DLSite]