A sidekick (usually some kind of animal) who, unconditionally, is extremely loyal to you. You have done nothing special to earn this loyalty, it just really really likes you.
From the relationship between Hibari and Hibird from Katekyo Hitman Reborn
Person 1: Dude why does that dog keep following you?
It's named after a person in town in the middle of North Island, New Zealand Turangi's most menacing "Hihira" they think he is the most displeasing person to ever walk the planet which is why they use his name for terms commonly used for being a weirdo/idiot/wannabe