Much like Pluto, Chibiusa's relationship with Hotaru is much darker in the manga because of the manga's much darker feel. Like Pluto, Hotaru was a child with no friends and no prospects of friends. She lived a lonely life with no one to comfort her until Chibiusa came cha-cha-ing in with all the good spirits she could muster and continued to attempt to be Hotaru's bestest friend even after Hotaru at first rebuffed her.
Also like Pluto, Hotaru is very protective of Chibiusa and would gladly lay down her life to protect her. Through Chibiusa Hotaru finds the strength inside her: the strength of Saturn, the strength to protect as well as destroy and recreate. Hotaru manages to throw off the overwhelming power of Mistress 9 because she loves Chibiusa and wants to protect her. Chibiusa has a natural grace and spirit (like her mother) that inspires others to be their best even when she's just being natural around them.
Unlike Pluto, Saturn remains very close to Chibimoon even after accepting her duties. In fact, it seems that Saturn may be a part of Chibimoon's court along with the Amazon Quartet, given the way she behaves during the coronation ceremony after the defeat of Neherenia. She and Chibiusa also remain close girl friends and school friends.