There are three books in the series.
They are meant for elementary school children and have furigana on all kanji, so you can focus on learning the key phrases, which are always in red text when they get used.
Unfortunately, they are a little pricey as far as manga go, at 918 yen per volume.
You can read a few sample pages on the website.
These kinds of things are not a priority for non-natives, but it’s cool to see that kind of resource on a general ebook site.