A young man volunteers to help test some cybernetics at a fully automated research facility.
Unfortunately the AI that runs the facility mistakes his consent to “help with a few implants” as consent to keep helping with a few more implants and he is quickly rendered unable to object.
The young man is temporarily unable to move or sense things as the new cybernetics take a moment to reroute his thoughts through them. Meanwhile his mobility is both restricted and upgraded at once.
As he regains control through the cybernetics he begins to struggle, but unfamiliar with how to move now, he cannot escape as the last parts are added to him to protect him from any harm. The helmet locking into place to “help” manage all his new robot parts.
The helmet helps too well. It is controlling all the mechanical parts, leaving the young man trapped as he stands on all fours at attention. But the helmet must ensure that all is integrated. And so a pixelated smile returns to the visor of the new Neko-Bot as its core component is taught that there is no other purpose than serving others. And looking cute while doing so.

Art by  Hydez
Description by me, maybe a little darker than Hydez originally intended so if you prefer, then maybe the young man is only temporarily encased.