I believe it's important Oz-san aspires to be himself... Not Gil-san.

However, if Oz-san wants to be tall... he could... perhaps...

[Cube clears his throat. Being serious and a bit timid about asking such a thing]
Would Oz-san be willing to let me test it on him in the end? I can't test it on myself, because I know the spell works on me. It'd help me greatly if you would let me test it on you... then you can be an adult and I will know it works.