From TheGamer: “On your first visit to Seafront in Nier Replicant, you’ll be introduced to the grumpy old Lighthouse Lady and be forced to help her out in retrieving a letter from the post office. This character goes on to feature in three different quests, one of which poses a moral issue where players must decide what to do.”
Source: N4G PC Nier Replicant: Lighthouse Lady Quest Walkthrough