Despite all the numerous times that Kentaro Miura’s Berserk has been adapted into anime, two arcs are nearly always left out: the introductory ‘Black Swordsman’ arc, as well as the subsequent ‘Lost Children’ arc.
In the Black Swordsman’s case, it sort of makes sense. Coming at the very beginning of the series, it takes place not only chronologically after the next arc, but also pales in comparison to the type of storytelling that Kentaro Miura would employ thereafter. But in the Lost Children’s case, this is a shame: not only does it tell an excellent story, it also serves an important function in the narrative that could benefit future adaptations.
Primarily of concern here are the 1997 TV anime and Millepensee’s hated Berserk (2016). This does not mean that the other adaptations are not worth talking about, but simply that they relate directly to the absence of Lost Children.

Both TV series open with a rendition of Puck and Guts’ first meeting. None of them are exactly the same as the manga, but they do at least pay some sort of homage to that event from the Black Swordsman arc. That same honor, however, is not afforded to Lost Children: instead, any time that an adaptation has proceeded beyond the Golden Age arc, it has conveniently forgotten that the Lost Children arc even exists.
The fact that both Berserk 1997 and Berserk 2016 touch upon the Black Swordsman arc, if only for a moment, should clue us into why so many adaptations have skirted around Lost Children: either the writers or the studio do not see much point in adapting it. Puck is undoubtedly a key character in the narrative going forward, while many of the characters introduced for Lost Children don’t live past the bounds of the arc. There is, therefore, a more pressing need to explain where Puck comes from, but not necessarily Jill and Rosine.
Technically speaking, the Lost Children arc is just one ‘chapter’ of the wider Conviction arc. Yet, I would say that it deserves to be classified as its own, separate arc: not only does it tell a largely self-contained story, it also feels out of place when placed next to the ‘Binding Chain Chapter’ and ‘Birth Ceremony Chapter.’
In any case, it is simply not true that adapting the Lost Children arc would have no merit. First of all, it serves an important purpose in getting the reader reacquainted with ‘Guts, the Black Swordsman’ – after spending so much time with him during his more carefree youth, surrounded by friends, you need that reset.
Furthermore, the Lost Children arc is beautiful. Aside from Guts’ journey as a whole, it constitutes perhaps some of Kentaro Miura’s best writing – not having it brought to screen seems like a disservice.
Taking place amid Guts’ wanderings before his encounter with the Holy Iron Chain Knights, the Lost Children arc follows the story of Jill and Rosine, two friends enamoured with the tale of an elf called Peekaf.
You can read the full story via the wiki, but what is important is how it relates to the events of Lost Children. Critically, it provides the inspiration for Rosine, the main antagonist of the Lost Children arc, to run away and become an Apostle – but it is much more than that. Very clearly, it is also a metaphor for the loss of childhood innocence; in our haste to grow up, we often rush away to find answers and only realize what we had once it has gone.

Jill and Rosine had painful lives. Both of them were beaten and abused by their fathers, which is why they were so transfixed by the idea of running away to a magical place. But as Guts says: “There’s no paradise.” There’s just grim, dark reality, and averting your eyes from it won’t do you any good.
Berserk can be a tough series to stomach. It is also a series with some questionable ideas. But it is, at its core, a tale of hope: the tale of one man fighting against all the odds to avoid his fate. The Lost Children arc is a perfect encapsulation of that, and deserves so much more appreciation.
You can pick up Berserk via Dark Horse.