The first arc is about 2 couples of incest brother-sister.
Adult, Incest, Serialized, Anal, Romance
Brother and Sister, Paizuri, Glasses, Blow job, Creampie, School Girls, Sex Toys, School Intercourse, Blackmail, Defloration, Threesome (MMF), Double Penetration, Foursome
The series OSTU has been categorized as 'Adult', therefore may contain intense violence, blood/gore, sexual content and/or strong language that may not be appropriate for underage viewers. So if you're under the legal age of 18, please go back.