I should also consider if there's a specific reference the user is missing. Maybe it's a very obscure title or a mix of elements from different sources. Providing general information on doujinshi about these themes would be helpful. Emphasize that the content is user-generated, so variety exists, and suggest that searching in Japanese with correct terms might yield better results. Finally, encourage the user to check official sources or fan communities for precise information if this is a known work.