Via the official website, the collaboration between Steins;Gate, Hello Kitty, and other Sanrio characters has begun. Here is a direct link to the first part of the prologue.
It appears as though the nature of this collaboration, which is the sixth of ten projects in the Steins;Gate 10th anniversary project series, is a web-based visual novel that will be released in parts on a weekly basis. As reported previously, this story takes place on a previously unexplored worldline, 0.549111%.
As of April 9, 2020, the second part to the prologue has been released.
As of April 16, 2020, the third part to the prologue has been released.
As of April 23, 2020, the fourth and final part to the prologue has been released.