You already wrote about character skills changing according to how much that character is bound or transformed. When I got it right this is based on the class a character gets from being bound. This is a nice idea and I‘m looking forward to see it in action. I‘m not fully sure how the class change mechanism works. Do characters get experience while fighting bound or does it just depend on how many items a character has equipped?
Perhaps there is a way to expand a bit on this idea. It should be very difficult to swing a sword while your arms are bound in an armbinder or kick while your legs are tied. So it would make sense, if certain skills would be replaced by a weaker version depending on the bondage items the character is wearing. For example the slash skill of a warrior could be replaced by a tackle skill. Once the character has sufficient experience being bound, she could then become a specific bondage class with better skills.
As an example the warrior class could become the ero tank class, with little offensive power but strong damage absorbing and preventing abilities.
This could be a skill set for this class:
Bump: Run into an enemy and deal little damage. Has a small change to unbalance the enemy. Physical: 2-3 damage; Physical: 000x||xx00; adds distraction 20% chance
Moan of courage: Moan loudly and buff your allies. Increases the damage of your allies. Targets all allies: xxxx||xxxx; adds strength (weaker version of the current buff)
Meat shield: Place yourself between the enemy and your team to protect them from attack. Target one ally and one enemy in the first position: 00xx||xxxx; Taunts one enemy, adds guarded to one ally, adds block to self
Masochism: The next time you receive damage, you are healed by twice the amount, but your lust also increases. Target self: 0xxx
Here are two links for example images as inspiration.
https://www.deviantart.com/uberis/art/The-TANK-924929622
https://www.deviantart.com/lurkx/art/Orchid-The-Witch-s-Assistant-Explained-950199915
Hopefully I found something you have not seen before, even though I think that is a bit unlikely.