User blog comment:DiegoAnime3000/RWBY Volume 3 Opening Scene is complete/@comment-25405817-20150612142856/@comment-9464517-20150615134652

Yeah, sometimes an anime will just jarringly change its theme song for the hell of it. Sometimes the new one is better (e.g. Death Note), sometimes it's worse (e.g. Spice and Wolf, Future Diary), sometimes there will be multiple intro changes of varying quality (e.g. Fullmetal Alchemist: Brotherhood).

On the other hand, some shows just have one theme song and stick it through to the end (e.g. Cowboy Bebop, Neon Genesis Evangelion, Trigun etc.).