Guts and the Band of the Hawk are attracted to this ritual by their supposed friend and leader Griffith who would like to be a part of the God Hand in pursuit of his lifelong ambition of Elden Ring Runes becoming the ruler of his own world-spanning kingdom.
What the Eclipse accomplishes is to provide a gateway to an alternate plane of existence, wherein God Hand God Hand receives the inductee's sacrifices (in Griffith's instance the sacrifice of the sacrifices of his Band of the Hawk soldiers) and transforms them into a demonic entity. Those unfortunate enough to be taken to this level will be welcomed into a huge, bloody area populated by hellish creatures, which is pretty much what I'd call the Elden Ring players in Caelid.
I'm combining two items here as I'm not able to justify writing separate entries to cover both.Before the Eclipse is welcomed into the realm of God Hand the man who was once called Griffith endures an entire an unending year of torture sleeping with the princess from an important kingdom. His tongue is severed and his skin is cracked, and all the while being required to wear an iron mask. After being saved by Guts and the others of the Band of the Hawk, Griffith slowly recuperates, but the mask remains to conceal the scars of his brutal incident.
Elden Ring players have drawn comparisons between Griffith's iron mask and the one of the Prisoner class players can select at the start on the first day of play. It's not a 1:1 reference obviously, but the mask's eye covering on the Prisoner's headwear neatly corresponds to the fact Berserk rarely depicts a front-facing Griffith in his mask, preferring to depict the tortured mercenary wearing a mask with one eye obscured from view by the mask's shadow.
Furthermore, the Winged Helm worn by Elden Ring boss Malenia and eventually obtainable by players can easily be seen as an homage to a similar piece of armor Berserk antagonist-turned-ally Farnese wears during her time commanding the Holy Iron Chain Knights. This could certainly be waved away as both being inspired by medieval depictions of Valkyries however I prefer to buy Elden Ring Runes view them as directly connected because this is more entertaining.