What is a word or good phrase for when you like someone, but there are no specific attributes you like about them? The reason you like them is just unknown.
"There is something about [X]" is a useful phrase, although it can have positive and negative connotations (i.e. it is neutral):
There is something about Mary that makes me like her.
There is something about Freddie that makes my skin crawl.
The default connotation probably depends on context: