Inma Sakusei ~Succubus ni Shihai Sareta Gakkou de~

July 1999.
Nostradamus predicted the rise of a dreadful power,
but it was just another day for many people. Nobody thought twice
about this month, except one: the protagonist, who one day after
school was suddenly transported to a world of demons.
His whole school had been swallowed into this world.
Classmates were slurped of their lifeforce by sex vixens...
Five survivors huddled together... can this tiny group of
boys and girls survive the sexpocalypse and get back home!?

[From DLsite English]