Yuji Naka has confirmed that he is no longer working for Square Enix as of April this year, and may not work in games again. As he wrote on Twitter, via Google Translate, "I can't talk about the reason now, but I hope I can talk about it when the time comes. As for future activities, I'm 55 years old, so I may retire."
Yuji Naka came up with the prototype for a smoothly scrolling platformer that became the original Sonic the Hedgehog, which he programmed in 1991. As a programmer, producer, and designer he worked on Sega games like Phantasy Star, Puyo Pop Fever, and many of the Sonic sequels. He was the last of Sonic's original creative team to leave Sega, founding his own studio called Prope in 2006.
In 2018, Yuji Naka joined Square Enix to serve as director on Balan Wonderworld, a 3D platformer that was his first collaboration with fellow Sonic co-creator Naoto Ohshima since Sonic Adventure in 1998. It launched in March of this year, but response was muted even after strobing effects that could cause seizures were patched out. It currently has a rating of "Mixed" on Steam.