I occasionally buy stuff off Rakuten. It’s mostly just herbs, but gradually points do build up. I also have a Kobo Libra reader. Kobo is a subsidiary of Rakuten, so you can log in with a Rakuten account and all that “integration.”
The other day I noticed that finally the newest volume of No Game No Life came out, so I went to get it. That took unexpected effort. The payment process just kept failing with an extremely unhelpful “we can’t complete this transaction” error. Naturally it wouldn’t say what was wrong, even though as it turns out it was their system’s brainfart.