Board Thread:Questions and Answers/@comment-5815126-20180222022045/@comment-34963928-20180311050919

He is the protagonist of the Dark Continent arc, a side protagonist in the YorkNew arc and shares the deuteragonist role with Leorio in the Hunter Exam arc. He is absent for most of the series but acts mostly on his own so I would say side protagonist while Killua is the Deuteragonist.