Eld Gin attends Attack Junior High as a second-year student and belongs to the unsanctioned Scout Regiment club. He possesses neatly tied-back blond hair, golden eyes, and wears a blue hoodie under his school uniform. Exhibiting a calm, level-headed personality, Eld serves as the voice of common sense within the club, making rational decisions during school activities. He frequently plays handheld video games, indicating his interest in gaming.

Eld maintains a close friendship with Gunther Schultz; the pair are often seen together. They jointly tease fellow club member Oluo Bozado about his studying habits, countering Oluo's claims of effortless success by revealing he actually crams half the night before tests. When Oluo suffers a self-inflicted tongue injury trying to block first-year students from the club room, Eld initially expresses concern and suspects foul play before learning the truth. Alongside other second-years, Eld disciplines first-years like Jean Kirstein for behavior and appearance, resulting in group cleaning punishments.

He joins classmates in accepting a Sports Day challenge against third-years. During the shoulder wars event, Eld helps carry Petra Ral alongside Oluo and Gunther. After the competition, he assists underclassmen with cleaning the court. For the "Test of Courage" event targeting new club members, Eld and Gunther dress as Titan models, hiding in the science room to scare first-years and later participating in a chase through the gym before revealing themselves.

At the school festival, Eld waits in line with classmates at the first-years' food stand. When Armin Arlert arrives in a sales outfit to take their cheeseburger order, Eld reacts with visible surprise and blushes alongside Gunther. He later watches Ilse Langnar's broadcast of Eren Yeager's mission to retrieve a cheeseburger from the principal's office. Eld's relationships center on his friendship with Gunther and interactions with fellow second-year Scout Regiment members Petra and Oluo.