While growing tweens/teens can become physically able to have sex and even reach near to their adult physiology sooner rather than later, the issue is always one of consent. Laws against minors having sex with adults are not meant to ignore that such arrangements can sometimes work out without seriously damaging the minor in various ways, but instead recognize that the starting point is always one of a power imbalance. This is also, in part, the fundamental claim against incestuous relationships.
And, that is all that we should find relevant to discussions of DMD - there are no underage characters here.
But, the power imbalance aspect has been there all along and it's up to the players to decide how D has been manipulated (or not) and to what possible extent by the MC, her friends, etc. - plus, what might the effects of her ongoing relationship with the MC mean to her in the long term. Is she truly feeling a growing and equal love with the MC or is it one that is also from conditioning of loving her provider/parent (i.e., that power imbalance thing)?
I look at the story from the character's perspective, in their own universe as it's presented, first - then, I take a step back to see what I think it could mean in our world's terms.
Thus far, the sheltered D has been influenced by the MC and both were attracted to each other - sincerely - but for different reasons, I feel. By this point in the VN, revealing more of the dynamics within their relationship through Chapter 3 could also talk to how D's growing independence of thought, spirit and action could help to reveal just how much the MC manipulated her power-imbalance-imbued affection for him that we've only thus far been able to guess at. It may be that D realizes this has happened and can live with it by virtue of all their shared experiences eventually leading to a detente of mutual understanding and respect of where they end up by the end of the game ... or, it may be that some threads and questions remain open for us to consider what it might mean for their relationship and D's well-being post-DMD.
What I think about their dynamic and how it maps into our real world doesn't really matter too much in relation to their own story, because Donutistan, etc. is a different place with a unique culture that isn't our world. But, we could still wonder about what their fictional example might say about situations with shared aspects in our world as comparison/contrast, because the best fiction does make us question how it might inform aspects of our own lives, IMHO. It's rarely a direct line of relation, but movements of ideas and values are always fair game to consider and debate from the example of a provocative fictional tale.
