Although no romantic undertones are evident in either the manga or anime, and their relationship skirts around the term 'friendship', there is a firm sense of mutual respect between Eren and Levi built up over the course of the manga and the two clearly care for each other's wellbeing. On Eren's side, Captain Levi of the Survey Corps represents everything he's come to admire and respect: freedom from the claustrophobic outer walls, hatred of titans and a desire to avoid the fate set out for him when Eren enquires about Levi's past, Petra informs him that he was previously a thug in the underground city. The start of their relationship in canon is thus dominated by Eren's hero-worship, and Levi's belief that Eren is little more than a monster with the potential to become an asset to humanity's cause. After being taken into custody, Levi shortly asks Eren "what is it you want to do? Eren's attitude towards titans interests Levi enough that he decides to take responsibility for him, vowing that if he "betrays us or goes berserk, I'll kill him on the spot.