It occurs to him gradually that Captain Levi is small.
It takes months for the nerves to go away, for the uncomfortable flutter in the pit of his stomach when Captain Levi turns flat eyes on him to settle. It takes almost a year for him to be even somewhat comfortable around Captain Levi.
And it takes three years for Eren to come out of the worst of his adolescence and grow another four inches and realize that Captain Levi is small.
He wakes up one day and heads down into the kitchen to grab food and Captain Levi is there, pressed on his tiptoes, reaching into one of the cabinets for the tin of loose tea leaves that gets gradually passed around between Survey Corps members. Eren plucks it off its shelf for him and is started when Captain Levi has to look up to quietly thank him.