Gyarugewe no Sekai yo, Youkoso!

Takenori is a major fan of Dating Sims. One day, he receives a strange eMail that tells him he can be the main character and asks him to insert the source material for his new world. Takenori inserts his favorite Dating Sim "Eternal Innocence" and after strange things he mistakens for a dream, wakes up - to find that all the heroines from Eternal Innocence have come to life in his usual surroundings!