Succubus Research Diary

A remake of Tsui no Sora included in the 10th anniversary Subarashiki Hibi package, including a fully rewritten script that is 1.5 times the size of the original and a "whole new work of its own".

The protagonist, “Leon,” spent his childhood in an orphanage in a rural village with other orphans, the girl “Sara” and the boy “Jake.”
However, they eventually part ways. Years later, as an adult, Leon coincidentally reunites with Sara, who has grown into a beautiful and voluptuous woman.
Conflicted by the changes but comforted by their childhood bond, Leon decides to live with Sara.
Initially reserved, Leon gradually accepts living with Sara, whose essence remains unchanged from their past.
Little did he know, there was another side of her hidden from him.

Remi was a Demon Lord who barely fulfilled her duties, spending every day lazing about.
One day her underlings had enough of her attitude, cast a weakening curse on her, and drove her out of her castle.
To lift the curse, Remi needs the 4 dispel gems each of her underlings keeps close to them. She must siege her own castle, undoing the curse as she climbs its steps...
Will Remi be able to regain her power, and the comfortable life she once had?

What happens when a hero falls for the demons he's supposed to destroy? Strange circumstances bring a human hero together with three demons, and the four of them set out on the adventure of a lifetime. They don't work well together at first, but after a while (and with a little help from a special item), these old enemies will start to REALLY get along...
 
The year is 1887.
Humankind has been assailed by demonic invaders from hell. For a time, humanity's future was uncertain... until brave soldiers arose who fought back the demons. These soldiers are called heroes.

One such hero, a man named Theo, has a goal in mind: take back the city of Manc from the demons who control it, the Halfas family. But the daughters of said family ended up being a lot cuter than he expected...