1. FANZA (formerly DMM) – Digital Rental/Purchase
2. Amazon Japan – Physical Blu-ray (The "Exclusive" Steelbook)
3. Root of all Evil (Defunct) – Nutaku / Fakku including less common titles. However
There is a common point of confusion here. The original Kuroinu hentai anime series (produced by Pink Pineapple) has two main "episodes" that cover the first visual novel, plus additional side episodes.
To be precise:
If you saw "ep 3 exclusive" mentioned somewhere, it was likely fan slang referring to the fact that Episode 3 (the sequel OVA) was not included in standard DVD box sets of the first two episodes and was sold separately. It is not a "lost" or region-exclusive episode.
Bottom line: No legal adult streaming service has a true "exclusive" on Kuroinu Episode 3. It's widely available on pirate sites because the official English licensing is fragmented (Media Blasters released some, but not all, episodes on DVD). availability can vary by region
The first and most recommended approach is to check official streaming platforms. Services like Crunchyroll, Funimation, and HIDIVE often carry a wide selection of anime series, including less common titles. However, availability can vary by region, and some platforms may not offer the episode for free.
"Kuroinu Kedakaki Seijo wa Hakudaku ni Somaru" is a Japanese title. When looking for information or episodes, it's often helpful to have the English title or a direct translation. The title translates to "The Noble Lady Trapped in a Dark Dungeon" in English. but not all