Magical Angel Creamy Mami Long Goodbye (OVA) 1985

Suffering from strange cramps in the stairwell, Yuu uncontrollably "ages up" into Mami:

She reverts after all the children have left the playground at dusk. Her shadow regresses down the slide:

Overnight, Yuu has aged up again into Mami in her bedroom:

She reverts again at the movie shoot. Fortunately, it happened behind the studio props while no one was watching:

Things are getting stranger and stranger fast. A perfect ending to the story: