One series that immediately comes to mind is 'The Idolmaster Cinderella Girls', though it's not strictly about triplets. It features a trio of blond-haired characters—Mika, Riina, and Fumika—who share a close bond, almost like sisters. Their dynamic is a blend of playful rivalry and deep camaraderie, which gives off serious triplet vibes even if they aren't biologically related. The show's focus on their growth as idols and the ups and downs of their relationships makes it a compelling watch for anyone who loves character-driven stories.
Another interesting pick is 'A Certain Scientific Railgun', where Misaka Mikoto has clones known as the 'Sisters'. While they aren't triplets, the sheer number of identical blondes (over 10,000!) creates a fascinating dynamic. The protagonist, Mikoto, is a fiery, strong-willed character with iconic lightning powers. The emotional weight of her relationship with her clones adds a layer of depth that's rare in action-focused anime. It's a great mix of sci-fi, drama, and heart.