This has been my first book in Japanese, read at about an N5 level with significant help from both a dictionary and WaniKani's book club thread. The book is rated for elementary 3rd and 4th grade, and is broken up into three short stories of 30-40 pages each with lots of super charming illustrations. I think it's a solid choice for people just starting out with native text, the grammar is mostly straightforward but natural and (as far as books at this level go) it has enough mystery to stay interesting.