The eclipse was the pivotal event of the series. volume 1-3 gave you a glimpse of the Black Swordsman. But volumes 4-14 gave you a flashback with Guts in the Band of the Hawk. In the anime it was the first episode shows you Guts fighting the Snake apostle and the rest of the episodes 2-25 shows you Gut's flashback. I watched the anime first and after about episode 6 or 7 I forgot that the story was a flashback. The first episode and volumes 1-3 are very fantastical with all the apostles and stuff. But from episode two on the story is very realistic so it makes the eclipse that much weirder, because Guts' life is as real as ours no monsters or the like, and then boom, the eclipse occurs (especially in the anime since Wild and the Skull Knight were taken out that eliminates the fantasy a bit.) So all of a sudden Guts, with a "normal" life, is taken into another dimension along with the hawks and sacrificed so the mangled Griffith can be reborn. That's why the eclipse is the pivotal and must shocking event in the anime and manga. Because the effect it has on Guts because there's (1)Normal Band of the Hawk Guts (2)Great Eclipse, and then (3)The Black Swordsman Guts fighting demons and apostles.
