To provide a comprehensive answer regarding the impact of the revelation about Eiji's grandfather on his quest, I would need to know the specific context or story you are referring to. Eiji and his grandfather could pertain to various narratives in literature, anime, or games.

If you could specify the title of the work or provide more details about the characters and their journey, I can offer a more tailored response. Alternatively, if this is a general inquiry about character revelations in storytelling, I can discuss how such revelations often serve to deepen character development, create emotional stakes, or alter the course of the narrative.

Please provide more context so I can assist you better!