Security could be a concern too—maybe a verification feature for counterfeit photobooks. A unique code inside that checks authenticity online. Or a loyalty program where owning the photobook gives you points or access to events. Maybe integrating with social media so fans can share their favorite photos with a hashtag, linking back to Nozomi's page.
Wait, the user mentioned "useful feature," so it should add real value. Maybe a language translation feature on the website, since some fans are non-Japanese. Subtitles for videos, or translated stories. Also, a way to submit fan mail that could be selected for future content. Or a digital scrapbook where fans can create their own pages using the photobook's content. photobook nozomi kurahashi 26 link
I should also consider the target audience. Fans often appreciate exclusive content, so linking to interviews, making-of videos, or acoustic versions of songs. Personalization features where users can input their name to get a custom message from her. Maybe a calendar with dates from the photobook, and reminders for events or her birthdays. Security could be a concern too—maybe a verification