Who Owns Your Voice? Japan's Top Voice Actor Clones with AI

Remember last year when OpenAI launched the ChatGPT voice feature and used Scarlett Johansson's voice without permission for the "Sky" voice? This sparked discussions about the implications of AI voice technology. After some legal intervention, OpenAI eventually removed "Sky." Recently, an Oscar-nominated film used AI to correct pronunciation, sparking debates in Hollywood about the rights to voice usage. We know faces are protected by image rights, but what about voices?

Famous voice actor Yuki Kaji, known for roles like Eren Yeager in "Attack on Titan" and Kirito in "Sword Art Online," is also concerned. His unique voice gives these characters their soul. In a 2023 NHK interview, he was shown an "AI Cover" mimicking his voice. He expressed that unauthorized AI generated content devalues the hard work of voice actors. Currently, he and other Japanese voice actors have formed a volunteer group called "NOMORE Unauthorized AI" to work with legal experts on proposals for "voice portrait rights."

This interview might make him seem anti-AI, but his stance isn't that rigid. He opposes unauthorized use. In the same year, to celebrate his 20th anniversary as a voice actor, Yuki Kaji launched a creative project called "Soyogi Fractal" (そよぎフラクタル).

If You Can't Beat 'Em, Join 'Em? Yuki Kaji's AI Voice Doppelgänger

The Soyogi Fractal project uses Yuki Kaji's voice as a base to explore various possibilities with AI, including voice synthesis. The name itself is meaningful. "Soyogi" (そよぎ) means a gentle breeze, symbolizing the free-flowing nature of sound. "Fractal" (フラクタル) refers to self-similar structures in mathematics, where the whole and parts are similar regardless of scale. This reflects Kaji's view on using his "voice" and his creative philosophy—"individuals form the whole, and the whole originates from individuals," akin to user-generated content (UGC).

Embracing this concept, he collaborated with the voice synthesis software CeVIO AI to create a virtual character based on his voice—"Soyogi Soyogi." Like Hatsune Miku, this character has a "personality." It can sing with synthesized voice, generate voice dialogues, and be used in multimedia creations like animation or game voiceovers, all within reasonable licensing. Encouraging creativity, he also hosts various contests to see how people can creatively use Soyogi.

Currently, you can download the "Soyogi AI" chatbot app to chat with Yuki Kaji's voice. The AI voice tone and expression change with emotions. There's even a custom alarm feature to wake you up with your favorite phrases from Soyogi every morning.

"Attack on Titan" Dream Team Reunites! Hajime Isayama Collaborates on "The Theory of the Evil Man and AI"

A highlight of the Soyogi Fractal project is Yuki Kaji's reunion with "Attack on Titan" creator Hajime Isayama. This time, Kaji isn't voicing a character but is involved in the concept. Together, they launched a buzzworthy official spin-off manga, "The Theory of the Evil Man and AI" (性悪男とAIのセオリー). This manga began serialization in February 2025 in "Bessatsu Shonen Magazine," becoming a cover and color page feature. Its release boosted the magazine's sales by 2.5 times.

"The Theory of the Evil Man and AI" is a short piece filled with satire and dark humor. The protagonist, "Soyogi," is exploited in a shady company and unexpectedly becomes a VTuber out of boredom. He skyrockets to fame but faces a slew of troubles, eventually leading becoming a threat to humanity's existence!

This is Isayama's first new work in 10 years since "Attack on Titan." He humorously noted, "Since I'm not doing the illustrations, I can include complex compositions I couldn't handle myself, as I can confidently leave it to others (he says while laughing)."