Kobo has their own flavor of epub called kepub. Readable as is (minus DRM) via any epub reader. The biggest difference is that it includes indexes that their ereaders use to track what page you are on, but are otherwise invisible unless you’re looking at the raw xhtml.
The Kobo Desktop app in combination with Calibre and the obok plugin (part of the NoDRM/DeDRM plugin) can easily strip the Kobo DRM and it outputs EPUBs.
This is what I use and is one of the easiest to remove from the books I buy. I’m happy to answer any other questions (I already bought this, I posted the original).