Bleach
This is the classic companion rec because both are long battle shounen with training, rivalries, rescue arcs, hidden organizations, and huge power escalations. Bleach swaps ninja villages for Soul Reapers, but the arc structure and character-driven fights feel familiar.
One Piece
One Piece shares the long-form adventure appeal: a young dreamer gathers allies, explores a massive world, and slowly uncovers deeper history. It is more pirate-comedy and less tournament/training focused, but fans of Naruto's emotional loyalty and big cast often connect with it.
Hunter x Hunter
Hunter x Hunter is recommended because of exams, young fighters, mentors, tactical abilities, and arcs that become much darker than the early tone suggests. It is more strategic and less sentimental than Naruto, but the coming-of-age battle-shounen structure overlaps.
Black Clover
Black Clover is basically a fantasy underdog shounen with a loud protagonist, a gifted rival, squad mentors, and a dream of becoming the top figure in society. Fans of Naruto's early emotional formula usually recognize the setup immediately.
My Hero Academia
Both focus on a powerless or underestimated boy entering a training institution, finding mentors, and chasing a symbolic top position. My Hero Academia uses superheroes instead of ninjas, but the school/team/rival structure is very Naruto-friendly.