Gave it a try and it was pretty fun. Very much reminds me of the Buxom mod for Slay the Spire which is a really fun mod. Expanding it out to other forms of growth is a good concept so I think you've got a solid project idea. My current question would be have you considered making the growth mechanics happen during combat instead of reaching a level and then the growth happens? The buxom mode had the growth happen during gameplay and personally I like that approach more but understand that may be a hard thing to implement, especially for muscle growth.
Also while I think the chibi's are cute is there any consideration of making the player character non-chibi? For the enemies I think it's fine but for the main characters I feel being chibi will make it hard to truly make them grow in their respective ways.
Good work so far though, everything seems programmed well and you have a sound concept going.