To find the content you may be looking for, refer to these "Episode 4" equivalents in other media: Content Equivalent Description Chapter 4: "A Certain Adventure"
Because the entire animated project concluded after these three total OVA releases, any claim of a "verified" fourth episode is likely referring to manga content or mislabeled videos on unofficial streaming sites. Content Breakdown by Format aki sora episode 4 verified
This chapter, and its follow-up Chapter 4.5 ("Some Like It Hot"), continues the story of siblings Aki and Sora. Aki Sora (2009) To find the content you may be looking