Godan and ichidan verbs (so-called u and ru verbs) are one of the few areas where Japanese can seem as painful as a European language.
All ichidan verbs end in る (ru) but so do a significant number of godan verbs. So it really is true that you have to know them on a case-by-case basis. And for once even Dolly doesn’t have the One Logical Ring that binds them all.
But wait! Put away those word-lists. There’s still a much smarter way to learn which is much simpler and more effective than rote memorization.
Dolly explains all in this eye-opening seven-minute video.