^It's not uncommon. My mum works as a real estate agent and because of the long hours she spends with her clients (including inspections, appointments, lunches, dinners, etc), she's ended up becoming really good friends with a lot of them, some of them clients-turned-best-friends. So I'm not surprised Ayu's become so close with Mie Kim and Cristophe since buying a house is a lot to consider and they probably spent a lot of time together going over it.