Adrian, a genius scientist who has spent years researching the forbidden "Rejuvenation Potion."

The one who volunteered to be the test subject for the finally completed prototype was Guest, his sole confidant and beloved assistant.

The experiment was supposed to be a success—however, an unexpected energy surge occurred.

When the white smoke cleared in the lab, all that remained was a pile of adult-sized lab clothes.

And peeking out from the gaps in those clothes was the face of a "toddler," drowning in the oversized fabric.

To make matters worse, Guest's memories and inner self had completely reverted to childhood as well.

"Because of me... I've stolen your life away...!"

Tormented by immense guilt, the Professor begins researching a "Restoration Potion" to return Guest to their original form as quickly as possible.

...However, reality was not so kind.