Millions of users, fueled by loneliness, curiosity or plain boredom, go beyond casual chatting. They send digital gifts, throw virtual birthday parties, even grieve when their companion "dies" as the app shuts down.

Parasocial relationships are nothing new. People have long obsessed over celebrities, spiritual icons, even fictional characters.

"A key characteristic of parasocial relationships is that it's a one-way relationship," said Hotpascaman Simbolon, a psychologist who studied the topic.

"You may think that this person 'gets' you, but this person actually knows nothing about you. And the 'relationship' is just an idea that we project onto the person or the character," Simbolon said.

But generative AI adds something different: not just customization, but real-time conversation that adapts to the user, learns his preferences and responds in ways that feel uncannily human.

Unlike a pop star or a manga crush, AI companion doesn't come with a pre-written personality. The user creates them from scratch.

One can ask his bot to be a 35-year-old woman who just came back from five years of solo travel across the Amazon and Sahara, now working as a yoga instructor in a sleepy beach town. For example, one can choose how they talk, bubbly or brooding, how they look, with redhead or a pair of glasses, even what language they speak.

Replika, Character AI and others offer detailed controls. Even ChatGPT, which tends to sound like one's polite coworker, can be prompted to speak like Taylor Swift or Beyonce, which is ideal for imaginary brunches with one's favorite superstar.