Going back to a few minutes ago—
Eren was lying casually on his seat inside the carriage, eyes glued to his handheld gaming console. He was completely engrossed in his gameplay, fully focused on a title called Oldest Ring, a very famous RPG game he used to play in his previous world. It was a well-known game with a dedicated fanbase, and one of his all-time favorites.
In the game, his character, known as The Exiled, was currently equipped with a long sword in one hand and a small shield in the other. He wasn't wearing any armor or clothing—just plain white underwear.
That's right. This was the barebones avatar Eren chose to challenge the first main boss of the game's story.