Levi had originally been stationed on the third floor, but with many awakened ability users still recovering their spiritual energy, he had moved down to the wall to fill the gap, ending up right beside Keith.
Their proximity, combined with their closeness in age, made it all too easy for a rivalry to spark. What Levi didn't realize, however, was that this was the first time he had initiated any sort of interaction with anyone; usually, he preferred to keep to himself.
Maybe it was because Keith was Kisha's brother that Levi had unconsciously lowered his guard around him. Or perhaps, by provoking Keith on purpose, he was simply trying to keep Keith focused on the zombies ahead so he wouldn't end up gagging his last meal out of fear.