Little Fatty thought Luo Yirui was very clever; after considering themselves familiar, he didn't start prying around, so he didn't mind hanging out with Luo Yirui.
What's wrong with hanging out with the Modern Family kids? They scoff at us, but I do it on purpose!
As for Jing Yuansi, she simply didn't care. It wasn't that she was indifferent by nature, she just wasn't very interested in anything related to Mystic Doctor. Little Fatty was close to Jing Yuansi, someone with extraordinary talent, yet she showed no interest in it.
The Pengge Sect had people happy and people sad.
Jing Yuansi really didn't care who she hung out with, as long as they could enjoy themselves together. But she was generally reluctant to play with kids from most sects. She approached Luo Yirui because he decisively rejected Lu Xuehan.
