Eren is Shingeki no Kyojin's protagonist. His childhood friend, Mikasa, notes on numerous occasions that he acts on impulse without thinking things through, and she often pulls/carries/throws him when he starts fighting with others to protect him from himself. Along with Mikasa, he tends to spend his free time with their mutual friend, Armin. His father is a doctor (whom is well respected by Hannes and potentially many more) whilst his mother is a housewife.

Mikasa is Eren's childhood friend, along with Armin. Mikasa shares an unbreakable bond with Eren following events in their past, and rushes to protect him whenever he is in danger. Mikasa possesses impressive fighting skill and strength even as a child. As a teen, Mikasa is considered a genius among all the army trainees and is incredibly skilled at combat and agility. She constantly worries for Eren's well-being and lives to protect him.