He'll squint and be suspicious when she first buys him food, but once he accepts that Robin is just a good person, he'll press her to let him do a job/solve a problem for her!! But also still charge her his standard fee of five cents because look this is a business he's running

He hangs out at the library every once in a while too (because it's free) so it might be fun if they could chat about books and learning sometimes!! Yato is a bright guy and fast learner but didn't really have a high school life because of home issues, so I thought it would be nice if he could interact with a good teacher figure...