IIRC in the original (the CG) as well as the VN adaptation, it's something Mia wanted to do with Mako after the director got beaten and turned into a puppet of Mako but Mako wouldn't let her little sister out because she believed that the outside world was "dirty", so uh after Mako gives Amamiya unlimited funds to develop very illegal and dangerous drugs, Mia basically takes one to go into "fairyland" (she has a low mental age)