1. doctor buys a demon slave and takes good care of him. though demon cannot speak much, he appreciates his "master" and wish to live for him. but as both of them fall in love, doctor is scared of his feelings so he sold the demon to a women who collects demons and have sex with them. demon felt betrayed and killed the woman. he then flee to the doctor for revenge but he couldn't do it. in the end, demon was beheaded but doctor went to save him and they ran away.
2,4. so cute. a human professor captured by a demon in the mountain and is now his "slave". he lived there with the demon for 5 years but went back to society when he saw him with a demon girl. but now prof. locked up and beat up becase the humans want to obtain the demon's power. demon come save him and declare to be his slave instead.
3. his mother keeps demons as playthings. he is in love with an older demon who took care of him when he was young and do anything to keep him. he slashed the demon's body in hopes the mom will throw the demon away but she sold him instead. he chases after the demon and ran away. demon was sold to doctor in first chapter.
5. extra chapter where all characters meet each other.
Mori no Koe