In Endless Night, the characters are stalked in their dreams by a mysterious woman in a bird mask, who ultimately turns out to be a sort of mental manifestation of
Romain's nightmares about the loss of his sister Chloé.
We later learn that the head doctor (Falco) did some unethical experimentation with icelotrophine on Romain, leading us to suspect that this ultimately gave him the ability to manifest aspects of his dreams in reality, such as Chloé. However, it is also noteworthy that doctors had been caring for Romain for years without being stalked by Chloé, whereas Romain only began to sleepwalk after Eva called his name, and Chloé only escaped when he touched Eva.
Did Romain gain the ability to make his nightmares into reality from the experimentation on him with icelotrophine? Did he have this ability originally, and the doctor's research was simply fruitless? Or was it all Eva's doing (unintentionally), with icelotrophine being a relatively mundane drug that simply induces waking dreams, and Romain never had any supernatural abilities until Eva made his dreams real?