Gentle Giantesses

Thanks, hehe.

The aging resulted perfect. And your idea is ok. But since Joana is still normal, there are three possiblities to make her grow:

-Cinthya becomes a Giantess, Blake and Rick use the growth substance on Joana, who had learned some of Blake's fighting moves after the events of the original story.
-Joana got the power to grow by will by consequence of the substance.
-Blaze and/or Seth and Nostory made Joana grow making use of that he was angry to Blake so she'd kill him (Not knowing she still loved him).

The action part I mentioned it could be combined with these ones. (Blake or others fight villains).

Blake could get stronger also if they used the substance on him (He was able to barely defeat Blaze after one dose of it). But as Rick would warn Blake, he must not overpass his body's limits, unless he trained harder each time, until reaching the physical limit (unknown in Blake, he had shown high resistance levels due to his fighting life). This could not be so important since the Giantesses have the main roles, XD... (It's just that part of Blake's style is that he takes care of himself most of the time).

If you want additional enemies, apart from Blaze who's the strongest and smartest, there's Cinthya, who would want to get revenge and ally to him (a GTS fight, for whose like tit)