TOKYO—Ryosei Takehisa, 24 years old, doesn’t have any children—unless you count an animated character with elfin ears called Mikuriya Kuon.

In live appearances on YouTube, the kimono-clad Kuon character, voiced by an actor hired by Mr. Takehisa, dispenses advice about the latest videogames and plays rock-paper-scissors with her fans.

The creator says he considers Kuon his “real daughter” even though she “resides within pixels.” While others may compete for fame or page views, “for me, I’m totally satisfied just with the fact that she was born and is continuing to live life in good health,” says Mr. Takehisa.

Digital avatars with human traits have long carved out a role on social media, on Instagram in particular. Japan, as it often does, has taken the idea and run with it, with its virtual characters now estimated to number more than 3,000.

Technology allows Kuon and her peers to have more direct engagement with fans—and sometimes a family-like relationship with their own creators. The characters, known as virtual YouTubers or VTubers because many are active on YouTube, sing and dance at live performances and answer questions on webcasts.