On the production blog for the series, a statement was made about the splitting of episodes into separate arcs which is worth pointing.
Previously, we were given the term which could be translated as “Lock Dealer Era”. It was speculated to be the title for the first 11 episodes, but the term is actually used when referencing Sigurd’s fighting style, saying that “his calm demeanor is something previously unseen during the time of Lock Dealers.” Credit goes to a user on HJU who pointed this out.
To the point, here is a rough translation of the production blog excerpt.
それでいうと、11話までが、「ビートライダーズ編」子供たちの世界の話。12話からが、「ユグドラシル編」。対 大人たちとの世界になります。
Subsequently, the first 11 episodes is a story about childhood, known as the “Beat Riders Saga”. Starting from episode 12, it becomes a story of adulthood called the “Yggdrasill Saga”.