Unlike the main series, which follows a linear narrative of dungeon crawling and party expansion, the OVA is designed purely as fan service—both narratively and visually—catering to the specific demographic that enjoys the franchise's explicit themes.
The production committee never announced an OVA because the show was controversial enough. Adding an OVA (which usually sells for $40+ for a single episode) would have been a risky financial move for a show that survived on Blu-ray pre-orders.
