Messenger From Dark Night

Hero is half-demon who has his demon part "dark night" awake every evening. Such person transfers to a new school that accepts half-humans as students.

The game can be called an adult sound novel. There are multiple branches and new branches open up after main branches clearance totaling 80 endings. Some of those endings have only slight differences, but just dig the number. The content is different for various branches, but it's not lovey-lovey, on the contrary it's rather dark and has multiple confrontations prepared. If it came out a bit later and was a bit more like a visual novel and not like a book, it would have all the chances to take away the pedestal of originator of visual novels from Leaf.