Biological creatures such as humans replace most their cells during their lifetime. The original cells that you had when you were born were all gone and had all been replaced a long time ago. So in this context, biological beings are pretty much like a Ship of Theseus, where every cell and tissue divides, dies off, and gets replaced by a new batch of identical cell or tissue.
For Ralph-sama, seeing this is a fantasy world, every fiber in his stufftoy body can plausibly be replaced for as long as its "function" as a soul vessel remains intact.