I’m using Bookwalker which is a online retailer ok books / ebooks, one of the biggest retailers.
Link to the book https://bookwalker.jp/dea471b7c1-8cdc-439e-b60d-e6c2762c0319/
They have a custom web DRM reader , but you can still select the text and using Rikai-chan to get meaning. They also have an mobile app, which is quite old but does work.
There are also other sites, as 小説家になろう, where light novels are free and content is real text in the web page, so you can use Rikai chan easily.
Link to Mushoku tensei 無職転生 - 異世界行ったら本気だす - - 第五十二話「米」
I read this book entirely in english but it was fun reading 6 chapters of it in japanese, but the number of new words per sentence was quite high ^^
You can also buy the kindle version on the japanese version of Amazon
And I got tips at how to conveniently look at words definitions with a kindle so maybe I’ll give it a try.