Basically, Nico kept glomping Maki until the latter girl got so used to it she no longer objected. Since Maki's really not touchy-feely, Nico and Rin are the two that give her some of that at school, and it helps break through her shell.
Well then I’m glad they’re there. And yes I did notice the expression that Maki held during the moment that Nico was hugging her from behind.