For Killua, he has two people he considers “sisters” in route, Mitsuki and Botan. At first Killua wasn’t sure what to make of her, she came off as a bit of a gossip. He doesn’t have a problem with it, since she is a great source for some juicy information. As time went on he got to know her a little bit at a time, he didn’t mind share a bit more about himself. On a interesting note finding out she was a death god, actually made him much more comfortable with being around her, go figure. She ended up reaching sis status when she comforted him when his best friend left. Being able to cuddle Killua is a privilege that few people get.