I think many people are confused when comparing e-book stores, but when you actually compare 17 different services, you'll notice there are quite a few differences.

To sum up, if you plan to use it regularly, ebookjapan is the safest choice. They distribute six 70% off coupons for first-time users, which makes it cheaper to buy multiple books through split purchases, and their discounts from the second time onward are more generous than others. They also have many weekend campaigns, so buying in bulk on weekends is a good strategy. The feature to display your bookshelf with spine labels is also subtly convenient.

However, if you want to read a large volume immediately, DMM Books is better. They offer a significant first-time discount, and manga and light novels always have a 25% point return. Buying 10 books at once is very cost-effective. But after the first purchase, the benefits are less substantial, so it's more suitable for short-term intensive reading.

If cost is your main concern, d-book is the way to go. They offer 20% cashback on the 10th, 20th, and 30th of each month, making ongoing use cheaper depending on timing. If you use d-points, it’s a good match. However, their viewer function is inferior to others, so don’t expect the best reading experience.

When comparing e-book stores, the key point is whether the first purchase is cheap only or if ongoing use remains affordable. Also, whether you mainly read manga or novels influences which service is best.

Comic Cmoa offers a 100% cashback of 1,000 yen on your first purchase, so you can read one book essentially for free. But after that, there are no special benefits, making it suitable for trial reading. For bulk buying, au Book Pass allows coupons for up to 100 books, which makes purchases cheaper the more you buy.

If you prioritize search functions and ease of purchase, BOOK☆WALKER is recommended. You can buy within the app, which is convenient. Kindle Store is only for those with Kindle devices, but it has a rare feature that shows estimated reading time, which is useful for people who want to manage their reading time.

Comparing e-book stores can be quite complicated, but ultimately it depends on how you use them. Will you buy just one book or several each month? Are you mainly reading manga or novels? The best service depends on these factors. Personally, if you plan to use it regularly, I recommend ebookjapan; if you want to get a good deal only on your first purchase, DMM Books or Comic Cmoa are good options.